Publications

Split superconducting and time-reversal symmetry-breaking transitions in Sr2RuO4 under stress.

V. Grinenko, S. Ghosh, R. Sarkar, J.-C. Orain, A. Nikitin, M. Elender, D. Das, Z. Guguchia, F. Brückner, M. E. Barber, J. Park, N. Kikugawa, D. A. Sokolov, J. S. Bobowski, T. Miyoshi, Y. Maeno, A. P. Mackenzie, H. Luetkens, C. W. Hicks, and H.-H. Klauss, Nature Physics 17, 748 (2021).

The muon spin rotation measurements report here have strongly supported the idea that the superconductivity Sr2RuO4 breaks time reversal symmetry (for example, with a spontaneous net angular momentum). Superconductivity that breaks time reversal symmetry is very rare, because it implies a frustration of the pairing interaction. It is a particularly intriguing possibility for Sr2RuO4 because it might only be possible with an altogether new form of pairing interaction; the fact though that we might need a new pairing interaction to explain this possible feature of Sr2RuO4 means that the standard of proof is high. In this experiment, we showed that the time-reversal symmetry-breaking transition splits from Tc when Sr2RuO4 is placed under uniaxial stress, which shows decisively that this transition cannot be some type of artefact of the superconducting transition.

Relationship between transport anisotropy and nematicity in FeSe.

J. Bartlett, A. Steppke, S. Hosoi, H. Noad, J. Park, C. Timm, T. Shibauchi, A. P. Mackenzie, and C. W. Hicks. Phys. Rev. X 11, 021038 (2021).

Electronic nematicity is a spontaneous reduction in the rotational symmetry of a system due to electronic interactions. At high temperatures, FeSe is tetragonal, but then at the nematic transition temperature Ts = 90 K a spontaneous anisotropy between the x- and y-axis conductivities appears. Why this occurs is not known, and one of the motivations to understand is that high-Tc superconductivity may be linked with nematicity. Here, we applied large strains to FeSe, in spite of it being a material that peels apart easily. We showed that the dependence of the resistive anisotropy on the strain-induced nematicity might not be consistent with one of the popular theories of its origin, that it is driven by spin fluctuations.

A proposal for detection of absolute rotation using superconductors and large voltages.

E. M. Forgan, C. M. Muirhead, A. I. M. Rae, and C. C. Speake. Physics Letters A, DOI: 10.1016/j.physleta.2020.126994

Consider rotating an electrostatically charged metal cylinder about its axis. The charge on the cylinder constitutes a solenoidal current, so the rotation induces a small magnetic field along the axis of the cylinder. This magnetic field is proportional to the absolute rotation rate of the cylinder relative to the rest of the Universe, so in principle it is possible by this means to measure the rotation rate of the Earth without looking out at the stars. In this paper, we consider how to do this in practice, making use of the properties of superconductors in screening magnetic fields, flux quantisation and SQUID detectors of very small fields. Collaborators in Padua (where Galileo worked) are constructing apparatus to test this idea.

A tunable stress dilatometer and measurement of the thermal expansion under uniaxial stress of Mn3Sn.

M. Ikhlas, K. R. Shirer, P.-Y. Yang, A. P. Mackenzie, S. Nakatsuji, and C. W. Hicks. Appl. Phys. Lett. 117, 233502 (2020).

Piezoelectric-based uniaxial pressure cell with integrated force and displacement sensors.

M. E. Barber, A. Steppke, A. P. Mackenzie, and C. W. Hicks, Rev. Sci. Inst. 90, 023904 (2019).

In the above two articles we describe methods for performing stress-strain measurements on correlated electron materials. Stress-strain measurements are standard in mechanical engineering, but it is an unexplored area of experimentation in condensed matter physics. Reasons include the need to operate at cryogenic temperatures, and the large strains that are sometimes required to qualitatively the alter the electronic structure of a material. The potential, however, is huge, because strain can be measured to extremely high precision. In these papers, we show that even a subtle change in magnetic structure generates measurable anomalies in the stress-strain relationship, and in these papers we show how to do these measurements.

Uniaxial pressure control of competing orders in a high-temperature superconductor.

H.-H. Kim, S. M. Souliou, M. E. Barber, E. Lefrançois, M. Minola, M. Tortora, R. Heid, N. Nandi, R. A. Borzi, G. Garbarino, A. Bosak, J. Porras, T. Loew, M. König, P. M. Moll, A. P. Mackenzie, B. Keimer, C. W. Hicks, and M. Le Tacon, Science 362, 1040 (2018).

Although we would all like to see a room-temperature superconductor, to understand the origins of high-temperature cuprate superconductivity it is often more valuable to try to suppress the superconductivity, and to see what other electronically ordered states can emerge. Here, we show that in-plane uniaxial stress can weaken the superconductivity of YBa2Cu3O6.67 and induce charge density wave order. The proximity of charge density wave order to superconductivity may provide a hint on the structure of the superconducting state.

Strong peak in Tc of Sr2RuO4 under uniaxial pressure.

A. Steppke, L. Zhao, M. E. Barber, T. Scaffidi, F. Jerzembeck, H. Rosner, A. S. Gibbs, Y. Maeno, S. H. Simon, A. P. Mackenzie, and C. W. Hicks, Science 355, eaaf9398 (2017).

In this paper we showed just how powerful a technique uniaxial stress can be. Under uniaxial compression, one of the Fermi surfaces of Sr2RuO4 passes through a Lifshitz transition (a change in Fermi surface topology), and as it does so the density of states peaks strongly. This happens when the lattice is compressed by about 0.5%– to see what that means technically, imaging taking a metre stick and pushing on it so hard that it compresses, elastically, by 5 mm. Right at the Lifshitz transition, there is a portion of Fermi surface where the Fermi velocity is almost zero. Tuning to this point causes Tc to more than double. Figure: Tc versus lattice strain in Sr2RuO4.

Magnetic-order crossover in coupled spin ladders.

M. Jeong, H. Mayaffre, C. Berthier, D. Schmidiger, A. Zheludev, and M. Horvatic, Phys. Rev. Lett. 118, 167206 (2017).

In the spin ladder compound known as DIMPY, we found a new type of crossover at very low temperature (~100 mK), below the ordering temperature of ≈300 mK. We interpret this as a dimensional crossover, which is unusual to observe below the ordering temperature. It maybe a consequence of an unusually large hierarchy in the exchange coupling network, due to frustrated interaction between the ladders. 

Dichotomy between attractive and repulsive Tomonaga-Luttinger liquids in spin ladders.

M. Jeong, D. Schumidifier, H. Mayaffre, M. Klanjsek, C. Berthier, W. Knafo, G. Ballon, B. Vignolle,   S. Krämer, A. Zheludev, and M. Horvatic, Phys. Rev. Lett. 117, 106402 (2016).

We found the first qualitative difference between the attractive and repulsive Tomonaga-Luttinger liquid using spin ladder materials. The results are in perfect agreement with the theoretical calculations using the DMRG data. The methodology developed here may apply broadly to one dimensional quantum spin systems. 

The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction.

E. M. Forgan, E. Blackburn, A. T. Holmes, A. K. R. Briffa, J. Chang, L. Bouchenoire, S. D. Brown, R. Liang, D. Bonn, W. N. Hardy, et al, Nature Communications 6, 10064 (2015).

Using a very versatile diffractometer at the ESRF synchrotron, we measure the intensities of the spots due to the spatially modulated ionic displacements. These intensities are about 10-6 of those due to the main crystal lattice. We deduce that the CDW action is in the CuO2 bilayers where superconductivity resides, and corresponds to a spatially varying doping in that region.

Attractive Tomonaga-Luttinger liquid in a quantum spin ladder.

M. Jeong, H. Mayaffre, C. Berthier, D. Schmidiger, A. Zheludev, and M. Horvatic, Phys. Rev. Lett. 111, 106404 (2013).

Using NMR relaxation measurements, we demonstrate a realisation of 'attractive' Tomonaga-Luttinger liquid (unlike more natural repulsive ones realised in electronic systems such as carbon nanotube) in a spin ladder compound. The field variation of the strength of the attractive interaction is also demonstrated.  

Direct observation of competition between superconductivity and charge density wave order in YBa2Cu3O6.67

J. Chang, E. Blackburn, A. T. Holmes, N. B. Christensen, J. Larsen, J. Mesot, R. Liang, D. A. Bonn, W. N. Hardy, A. Watenphul, M. v. Zimmermann, E. M. Forgan, and S. M. Hayden, Nature Physics 8, 871 (2012).

Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves. Several cuprates, including some that are superconductors, show spin and charge density wave order. However, these states have not been observed in all cuprates, calling into question the generality of the observation. In this paper, we observe charge density waves in a member of the YBCO family YBa2Cu3O6.67. Using the Birmingham 17 T cryomagnet on beamline BW5 at HASYLAB, Hamburg, we show that they are in competition with the superconductivity.

Magnetic flux lines in type-II superconductors and the ‘hairy ball’ theorem.

M. Laver and E. M. Forgan, Nature Communications 1, 45 (2010).

Many prominent phenomena originate from geometrical effects rather than from local physics. For example, the ‘hairy ball’ (HB) theorem asserts that a hairy sphere cannot be combed without introducing at least one singularity, and is fulfilled by the atmospheric circulation with the existence of stratospheric polar vortices and the fact that there is always at least one place on Earth where the horizontal wind is still. In this study, we examine the consequences of the HB theorem for the lattice of flux lines that form when a magnetic field is applied to a type-II superconducting crystal. We find that discontinuities must exist in lattice shape as a function of field direction relative to the crystal. Extraordinary, ‘unconventional’ flux line lattice shapes that spontaneously break the underlying crystal symmetry are thus remarkably likely across all type-II superconductors, both conventional and unconventional.

Exploring the fragile antiferromagnetic superconducting phase in CeCoIn5.

E. Blackburn, P. Das, M. R. Eskildsen, E. M. Forgan, M. Laver, C. Niedermayer, C. Petrovic, and J. S. White, Phys. Rev. Lett. 105, 187001 (2010).

The heavy-fermion superconductor CeCoIn5 has very unusual behaviour when a magnetic field is applied in the basal plane, and close to the high magnetic field edge of the superconducting region: magnetic order develops within the superconductor, disappearing precipitously when the superconductivity is destroyed. Here we investigate the changes to the order as the magnetic field direction is rotated away from the basal plane of the crystal and magnetic order is possibly replaced by FFLO order. Figure: field dependence of the magnetic peak, with a field angle of 12°. The magnetic order disappears at Hc2.

Observations of Pauli paramagnetic effects on the flux line lattice in CeCoIn5.

J. S. White, P. Das, M. R. Eskildsen, L. DeBeer-Schmitt, E. M. Forgan, A. D. Bianchi, M. Kenzelmann, M. Zolliker, S. Gerber, J. L. Gavilano, J. Mesot, R. Movshovich, E. D. Bauer, J. L. Sarrao, and C. Petrovic. New Journal of Physics, 12, 023026 (2010).

From small-angle neutron scattering studies of the flux line lattice in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field and temperature dependence of the spatial variation of the field in the mixed state. This extends our earlier work (Bianchi et al. Science 319 177 (2008)) to temperatures up to 1250 mK. Over the entire temperature range, paramagnetic magnetisation in the flux line cores results in an increase of the visibility of the flux lines with field. This is the opposite behaviour to that of conventional superconductors. Near Bc2, the field variation decreases again, and our results indicate that this fall-off extends outside the proposed Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing throughout the bulk, arising from the conflict between the anti-parallel alignment of the electron spins in this d-wave superconductor and the parallel alignment favoured by the field.

Superconducting vortices in CeCoIn5: toward the Pauli-limiting field.

A. D. Bianchi, M. Kenzelmann, L. DeBeer-Schmitt, J. S. White, E. M. Forgan, J. Mesot, M. Zolliker, J. Kohlbrecher, R. Movshovich, E. D. Bauer, J. L. Sarrao, Z. Fisk, C. Petrovic, and M. R. Eskildsen, Science 319, 177 (2008).

In this paper we demonstrated the effects of Pauli paramagnetism on the structure of the magnetic flux lines in the mixed state of a superconductor. CeCoIn5 is a d-wave superconductor and the Cooper pairs consist of heavy electrons with antiparallel spins. The alignment of the spins by an applied magnetic field magnetises the flux line cores and limits the upper critical field. We also see the effects of the d-wave pairing on the shape of the flux line lattice in this material.

Quantum Turbulence.

W. F. Vinen and J. J. Niemela, J. Low Temp. Physics 128, 167 (2002).

This review discusses turbulence in superfluids, which on a long length scale is similar to classical turbulence, but on a short length scale is altered by the quantisation of vorticity. Superfluids can host counterflow turbulence, in which the normal and superfluid portions flow in opposite directions, and which has no counterpart in classical turbulence.

Observation of a square flux-line lattice in the unconventional superconductor Sr2RuO4.

T. M. Riseman, P. G. Kealey, E. M. Forgan, A. P. Mackenzie, L. M. Galvin, A. W. Tyler, S. L. Lee, C. Ager, D. Mck. Paul, C. M. Aegerter, R. Cubitt, Z. Q. Mao, T. Akima, and Y. Maeno, Nature 396, 242 (1998).

The flux lattice of most superconductors is triangular, which is the arrangement that minimises the field energy. Here, using small-angle neutron scattering, it was shown that Sr2RuO4has a square flux lattice. This result shows that the superconducing gap in Sr2RuO4 varies strongly around the Fermi surfaces, which is a signature of unconventional superconductivity. This gap anisotropy is strong enough to overcome the natural tendency towards a triangular lattice.

Direct observation of magnetic flux lattice melting and decomposition in the high-Tc superconductor Bi2.15Sr1.85CaCu2O8-x.

R. Cubitt, E. M. Forgan, G. Yang, S. L. Lee, D. McK. Paul, H. A. Mook, M. Yethiraj, P. H. Kes, T. W. Li, A. A. Menovsky, Z. Tarnawski, and K. Mortensen, Nature 365, 407 (1993).

Using information from our µSR measurements in this material, we knew that evidence for much-sought melting of the flux line lattice required pushing our techniques to very low fields, at which the signal was difficult to measure. However, we managed to observe the flux line lattice inside a single crystal of Bi2.15Sr1.85CaCu2O8-x using small-angle neutron diffraction. The diffracted intensity went rapidly to zero at a magnetic field-dependent flux lattice melting temperature. This melting coincides with the appearance of finite resistance within the superconducting state. The flux lattice signal also disappeared at low temperatures, when a sufficiently high field was by applied, probably because of the decomposition of flux lines into two-dimensional 'pancake' vortices. Flux lattice melting may well limit the practical application of high-Tc materials at high temperatures.

Flux quantization in a high-Tc superconductor.

C. E. Gough, M. S. Colclough, E. M. Forgan, R. G. Jordan, M. Keene, C. M. Muirhead, A. I. M. Rae, N. Thomas, J. S. Abell, and S. Sutton, Nature 326, 855 (1987).

Within a fortnight of the publication of superconductivity above liquid nitrogen temperatures in yttrium-based cuprates, we were measuring the quantum of flux in this system, and found that the value was h/2e. This was the first demonstration that high-Tc superconductivity is due to paired electrons, just as in conventional superconductors. It was some time before it became clear that the pairing is d-wave, and not the original BCS s-wave, while the exact mechanism causing the pairing is still a matter of controversy more than 30 years later. Figure: output of a conventional SQUID magnetometer, measuring quanta of flux jumping in and out of a donut of Y-Ba-Cu-O high-Tc superconductor. The “Millikan-style” graph demonstrates the size of the quantum of flux in this material.

The nucleation of vorticity by ions in superfluid 4He.

C. M. Muirhead, W. F. Vinen, and R. J. Donnelly, Phil. Trans. R. Soc. Lond. A 311, 433 (1984).

When ions move through superfluid 4He, they can nucleate vortices, if their velocity exceeds a critical value. One possibility is that in the illustration here, that a whole vortex ring is created that trails the ion. Much more likely though is a vortex that begins and ends on the solid helium that is attached to the ion.

The motion of flux lines in type II superconductors

P. Nozières and W. F. Vinen, The Philosophical Magazine, 14, 130 (1966).

Vortices in type-II superconductors experience a Magnus force identical to that found in liquid helium. In combination with friction between the vortex core and the lattice, the Magnus force causes vortices to move sideways when strong current is applied to a type II superconductor.

 

The detection of single quanta of circulation in liquid helium II

W. F. Vinen, Proc. Roy. Soc. A260, 218 (1961).

Before being appointed as a professor in Birmingham, Joe Vinen made the first direct demonstration of a macroscopic quantum effect in any superfluid system, by observing quantised vortices trapped on a fine wire in rotating superfluid 4He.

2021 

I. Zivkovic, V. Favre, C. S. Mejia, H. O. Jeschke,  A. Magrez, B. Dabholkar, V. Noculak, R. S. Freitas, M. Jeong, N. G. Hegda, L. Testa, P. Babkevich, Y. X. Su, P. Manuel, H. Luetkens, C. Baines, P. J. Baker, J. Wosnitza, O. Zaharko, Y. Iqbal,  J. Reuther, and H. M. Ronnow, Magnetic field induced quantum spin liquid in the two coupled trillium lattices of K₂Ni₂(SO₄)₃. Phys. Rev. Lett. 127, 157204 (2021).  

D. Sun, D. A. Sokolov, R. Waite, S. Khim, P. Manuel, F. Orlandi, D. D. Khalyavin, A. P. Mackenzie, and C. W. Hicks, Heisenberg spins on an anisotropic triangular lattice: PdCrO₂ under uniaxial stress. New Journal of Physics 23, 123050 (2021). 

E. Campillo, R. Riyat, S. Pollard, P. Jefferies, A. T. Holmes, R. Cubitt, J. S. White, J. Gavilano, Z. Huesges, O. Stockert, E. M. Forgan, and E. Blackburn, Observations of the effect of strong Pauli paramagnetism on the vortex lattice in superconducting CeCu₂Si₂. Phys. Rev. B 104, 184508 (2021). 

M. Soda, N. Kagamida, S. Muhlbauer, E. M. Forgan, E. Campillo, M. Kriener, H. Yoshizawa, and H. Kawano-Furukawa, J. Phys. Soc. Japan 90, 104710 (2021). 

C. Lester, S. Ramos, R. S. Perry, T. P. Croft, M. Laver, R. I. Bewley, T. Guidi, A. Hiess, A. Wildes, E. M. Forgan, and S. M. Hayden. Magnetic-field-controlled spin fluctuations and quantum criticality in Sr₃Ru₂O₇. Nat. Communications 12, 5798 (2021). 

V. Grinenko, D. Das, R. Gupta, B. Zinkl, N. Kikugawa, Y. Maeno, C. W. Hicks, H.-H. Klauss, M. Sigrist, and R. Khasanov, Unsplit superconducting and time reversal symmetry breaking transitions in Sr₂RuO₄ under hydrostatic pressure and disorder. Nat. Communications 12, 3920 (2021). 

A. Chronister, A. Pustogow, N. Kikugawa, D. A. Sokolov, F. Jerzembeck, C. W. Hicks, A. P. Mackenzie, E. D. Bauer, and S. E. Brown, Evidence for even parity unconventional superconductivity in Sr₂RuO₄. Proc. Nat. Acad. Sciences 118, e2025313118 (2021). 

J. Bartlett, A. Steppke, S. Hosoi, H. Noad, J. Park, C. Timm, T. Shibauchi, A. P. Mackenzie, and C. W. Hicks, Relationship between transport anisotropy and nematicity in FeSe. Phys. Rev. X 11, 021038 (2021). 

V. Grinenko, S. Ghosh, R. Sarkar, J.-C. Orain, A. Nikitin, M. Elender, D. Das, Z. Guguchia, F. Brückner, M. E. Barber, J. Park, N. Kikugawa, D. A. Sokolov, J. S. Bobowski, T. Miyoshi, Y. Maeno, A. P. Mackenzie, H. Luetkens, C. W. Hicks, and H.-H. Klauss, Split superconducting and time-reversal symmetry-breaking transitions in Sr₂RuO₄ under stress. Nat. Phys. 17, 748 (2021). 

Y.-S. Li, N. Kikugawa, D. A. Sokolov, F. Jerzembeck, A. S. Gibbs, Y. Maeno, C. W. Hicks, J. Schmalian, M. Nicklas, and A. P. Mackenzie, High-sensitivity heat-capacity measurements on Sr₂RuO₄ under uniaxial pressure. Proc. Nat. Acad. Sciences USA 118, e2020492118 (2021). 

G. M. Klemencic, D. T. S. Perkins, J. M. Fellows, C. M. Muirhead, R. A. Smith, S. Mandal, S. Manifold, M. Salman, S. R. Giblin, O. A. Williams. Phase slips and metastability in granular boron-doped nanocrystalline diamond microbridges. Carbon 175, 43 (2021). 

H.-H. Kim, E. Lefrançois, K. Kummer, R. Fumagalli, N. B. Brookes, D. Betto, S. Nakata, M. Tortora, J. Porras, T. Loew, M. E. Barber, L. Braicovich, A. P. Mackenzie, C. W. Hicks, B. Keimer, M. Minola, and M. Le Tacon, Charge density waves in YBa₂Cu₃O_6.67 probed by resonant x-ray scattering under uniaxial compression. Phys. Rev. Lett. 126, 037002 (2021). 

S. Ghosh, A. Shekhter, F. Jerzembeck, N. Kikugawa, D. A. Sokolov, M. Brando, A. P. Mackenzie, C. W. Hicks, and B. J. Ramshaw, Thermodynamic evidence for a two-component superconducting order parameter in Sr₂RuO₄. Nat. Phys. 17, 199 (2021). 

E. M. Forgan, C. M. Muirhead, A. I. M. Rae, and C. C. Speake, A proposal for detection of absolute rotation using superconductors and large voltages. Phys. Lett. A, 386, 126994 (2021). 

C. Gough, Acoustic characterization of string instruments by internal cavity measurements. J. Acoustical Soc. America 150, 1922 (2021). 

2020 

J. Head, P. Manuel, F. Orlandi, M. Jeong, M. R. Lees, R. K. Li, and C. Greaves, Structural, magnetic, magnetocaloric, and magnetostrictive properties of Pb_1-xSr_xMnBO₄ (x=0, 0.5, and 1.0). Chemistry of Materials 32, 10184 (2020). 

M. Ikhlas, K. R. Shirer, P.-Y. Yang, A. P. Mackenzie, S. Nakatsuji, and C. W. Hicks, A tunable stress dilatometer and measurement of the thermal expansion under uniaxial stress of Mn₃Sn. Appl. Phys. Lett. 117, 233502 (2020). 

S. Ghosh, F. Brückner, A. Nikitin, V. Grinenko, M. Elender, A. P. Mackenzie, H. Luetkens, H.-H. Klauss, and C. W. Hicks, Piezoelectric-driven uniaxial pressure cell for muon spin relaxation and neutron scattering experiments. Rev. Sci. Inst. 91, 103902 (2020). 

Z. Guguchia, D. Das, C. N. Wang, T. Adachi, N. Kitajima, M. Elender, F. Brückner, S. Ghosh, V. Grnenko, T. Shiroka, M. Müller, C. Mudry, C. Baines, M. Bartkowiak, Y. Koike, A. Amato, J. M. Tranquada, H.-H. Klauss, C. W. Hicks, and H. Luetkens, Using uniaxial stress to probe the relationship between competing superconducting states in a cuprate with spin-stripe order. Phys. Rev. Lett. 125, 097005 (2020). 

J. Park, J. M. Bartlett, H. M. L. Noad, A. L. Stern, M. E. Barber, M. König, S. Hosoi, T. Shibauchi, A. P. Mackenzie, A. Steppke, and C. W. Hicks, Rigid platform for applying large tunable strains to mechanically delicate samples. Rev. Sci. Inst. 91, 083902 (2020). 

E. Jellyman, P. Jefferies, S. Pollard, E. M. Forgan, E. Blackburn, E. Campillo, A. T. Holmes, R. Cubitt, J. Gavilano, H. D. Wang, J. H. Du, and M. H. Fang, Unconventional superconductivity in the nickel chalcogenide superconductor TlNi₂Se₂. Phys. Rev. B 101, 134523 (2020). 

J. Choi, O. Ivashko, E. Blackburn, R. Liang, D. A. Bonn, W. N. Hardy, A. T. Holmes, N. B. Christensen, M. Hucker, S. Gerber, O. Gutowski, U. Rutt, M. von Zimmermann, E. M. Forgan, S. M. Hayden, and J. Chang, Spatially inhomogeneous competition between superconductivity and the charge density wave in YBa₂Cu₃O_6.67. Nat. Communications 11, 990 (2020).

2019

S. Kwon, M. Jeong, M. Kubus, B. Wehinger, K. W. Kramer, C. Ruegg, H. M. Ronnow, and S. Lee, Field-induced anisotropy in the quasi-two-dimensional weakly anisotropic antiferromagnet [CuCl(pyz)₂]BF₄. Phys. Rev. B 99, 214403 (2019). 

B. Mastracci, S. Bao, W. Guo, and W. F. Vinen, Particle tracking velocimetry applied to thermal counterflow in superfluid He-4: Motion of the normal fluid at small heat fluxes. Phys. Rev. Fluids 4, 083305 (2019). 

M. E. Barber, F. Lechermann, S. V. Streltsov, S. L. Skornyakov, S. Ghosh, B. J. Ramshaw, N. Kikugawa, D. A. Sokolov, A. P. Mackenzie, C. W. Hicks, and I. I. Mazin, Role of correlations in determining the Van Hove strain in Sr₂RuO₄. Phys. Rev. B 100, 245139 (2019). 

A. W. Pustogow, Y. K. Luo, A. Chronister, D. A. Sokolov, F. Jerzembeck, A. P. Mackenzie, C. W. Hicks, N. Kikugawa, S. Raghu, E. D. Bauer, and S. E. Brown, Constraints on the superconducting order parameter in Sr₂RuO₄ from oxygen-17 nuclear magnetic resonance. Nature 574, 72 (2019). 

D. Sun, D. A. Sokolov, J. M. Bartlett, J. Sannigrahi, S. Khim, P. Kushwaha, D. D. Khalyavin, P. Manuel, A. S. Gibbs, H. Takagi, A. P. Mackenzie, and C. W. Hicks, Magnetic frustration and spontaneous rotational symmetry breaking in PdCrO₂. Phys. Rev. B 100, 094414 (2019). 

V. Sunko, E. A. Morales, I. Markovic, M. E. Barber, D. Milosavljevic, F. Mazzola, D. A. Sokolov, N. Kikugawa, C. Cacho, P. Dudin, H. Rosner, C. W. Hicks, P. D. C. King, and A. P. Mackenzie, Direct observation of a uniaxial stress-driven Lifshitz transition in Sr₂RuO₄. npj Quant. Materials 4, 46 (2019). 

Y. K. Luo, A. Pustogow, P. Guzman, A. P. Dioguardi, S. M. Thomas, F. Ronning, N. Kikugawa, D. A. Sokolov, F. Jerzembeck, A. P. Mackenzie, C. W. Hicks, E. D. Bauer, I. I. Mazin, and S. E. Brown, Normal state O-17 NMR studies of Sr₂RuO₄ under uniaxial stress. Phys. Rev. X 9, 21044 (2019). 

J. Schmidt, V. Bekeris, G. S. Lozano, M. V. Bortule, M. M. Bermudez, C. W. Hicks, P. C. Canfield, E. Fradkin, and G. Pasquini, Nematicity in the superconducting mixed state of strain detwinned underdoped Ba(Fe_1-xCo_x)₂As₂. Phys. Rev. B 99, 064515 (2019). 

M. E. Barber, A. Steppke, A. P. Mackenzie, and C. W. Hicks, Piezoelectric-based uniaxial pressure cell with integrated force and displacement sensors. Rev. Sci. Inst. 90, 023904 (2019). 

2018 

M. A. Sorensen, U. B. Hansen, M. Perfetti, K. S. Pedersen, E. Bartolome, G. G. Simeoni, H. Mutka, S. Rols, M. Jeong, I. Zivkovic, et al, Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet. Nat. Communications 9, 1292 (2018). 

A. A. Bush, N. Buttgen, A. A. Gippius, M. Horvatic, M. Jeong, W. Kretschmer, V. I. Marchenko, Y. A. Sakhratov, and L. E. Svistov, Exotic phases of frustrated antiferromagnet LiCu₂O₂. Phys. Rev. B 97, 054428 (2018). 

J. Gao, W. Guo, S. Yui, M. Tsubota, and W. F. Vinen, Dissipation in quantum turbulence in superfluid He-4 above 1 K. Phys. Rev. B 97, 184518 (2018). 

H.-H. Kim, S. M. Souliou, M. E. Barber, E. Lefrançois, M. Minola, M. Tortora, R. Heid, N. Nandi, R. A. Borzi, G. Garbarino, A. Bosak, J. Porras, T. Loew, M. König, P. M. Moll, A. P. Mackenzie, B. Keimer, C. W. Hicks, and M. Le Tacon, Uniaxial pressure control of competing orders in a high-temperature superconductor. Science 362, 1040 (2018). 

C. A. Watson, A. S. Gibbs, A. P. Mackenzie, C. W. Hicks, and K. A. Moler, Micron-scale measurements of low anisotropic strain response of local T_c in Sr₂RuO₄. Phys. Rev. B 98, 094521 (2018). 

J. Park, H. Sakai, A. P. Mackenzie, and C. W. Hicks, Effect of uniaxial stress on the magnetic phases of CeAuSb₂. Phys. Rev. B 98, 024426 (2018). 

M. E. Barber, A. S. Gibbs, Y. Maeno, A. P. Mackenzie, and C. W. Hicks, Resistivity in the vicinity of a Van Hove singularity: Sr₂RuO₄ under uniaxial pressure. Phys. Rev. Lett. 120, 076602 (2018). 

J. Park, H. Sakai, O. Erten, A. P. Mackenzie, and C. W. Hicks, Effect of applied orthorhombic lattice distortion on the antiferromagnetic phase of CeAuSb₂. Phys. Rev. B 97, 024411 (2018). 

2017 

M. Jeong, H. Mayaffre, C. Berthier, D. Schmidiger, A. Zheludev, and M. Horvatic, Magnetic-order crossover in coupled spin ladders, Phys. Rev. Lett. 118, 167206 (2017). 

J. Gao, E. Varga, W. Guo, and W. F. Vinen, Energy spectrum of thermal counterflow turbulence in superfluid He-4. Phys. Rev. B 96, 094511 (2017). 

W. Tabis, B. Yu, I. Bialo, M. Bluschke, T. Kolodziej, A. Kozlowski, E. Blackburn, K. Sen, E. M. Forgan, M. von Zimmermann, Y. Tang, E. Weschke, B. Vignolle, M. Hepting, H. Gretarsson, R. Suharto, F. He, M. Le Tacon, N. Barisic, G. Yu and M. Greven, Synchrotron x-ray scattering study of charge-density-wave order in HgBa₂CuO_4+d. Phys. Rev. B 96, 134510 (2017). 

A. P. Mackenzie, T. Scaffidi, C. W. Hicks, and Y. Maeno, Even odder after twenty-three years: the superconducting order parameter puzzle of Sr₂RuO₄. npj Quantum Materials 2, 40 (2017). 

L. Shen, E. Jellyman, E. M. Forgan, E. Blackburn, M. Laver, E. Canevet, J. Schefer, Z. He, and M. Itoh, Unconventional magnetic phase separation in gamma-CoVO₆. Phys. Rev. B 96, 054420 (2017). 

D. O. Brodsky, M. E. Barber, J. A. N. Bruin, R. A. Borzi, S. A. Grigera, R. S. Perry, A. P. Mackenzie, and C. W. Hicks, Strain and vector magnetic field tuning of the anomalous phase of Sr₃Ru₂O₇. Sci. Advances 3, e1501804 (2017). 

A. Steppke, L. S. Zhao, M. E. Barber, T. Scaffidi, F. Jerzembeck, H. Rosner, A. S. Gibbs, Y. Maeno, S. H. Simon, A. P. Mackenzie, and C. W. Hicks, Strong peak in T_c of Sr₂RuO₄ under uniaxial pressure. Science 355, eaaf9398 (2017). 

2016 

M. Jeong, D. Schmidiger, H. Mayaffre, M. Klanjsek, C. Berthier, W. Knafo, G. Ballon, B. Vignolle, S. Krämer, A. Zheludev, and M. Horvatic, Dichotomy between attractive and repulsive Tomonaga-Luttinger liquids in spin ladders. Phys. Rev. Lett. 117, 106402 (2016). 

P. Babkevich, M. Jeong, Y. Matsumoto, I. Kovacevic, A. Finco, R. Toft-Petersen, C. Ritter, M. Månsson, S. Nakatsuji, and H. M. Rønnow, Dimensional reduction in quantum dipolar antiferromagnets. Phys. Rev. Lett. 116, 197202 (2016). 

J. Gao, W. Guo, and W. F. Vinen, Determination of the effective kinematic viscosity for the decay of quasiclassical turbulence in superfluid He-4. Phys. Rev. B 94, 094502 (2016). 

J. Gao, W. Guo, V. S. L’vov, A. Pomyalov, L. Skybek, E. Varga, and W. F. Vinen, Decay of counterflow turbulence in superfluid He-4. JETP Lett. 103, 648 (2016). 

C. M. Muirhead, B. Gunupudi, and M. S. Colclough, Photon transver in a system of coupled superconducting microwave resonators. J. Appl. Phys. 120, 084904 (2016). 

B. Gunupudi, C. M. Muirhead, and M. S. Colclough, In situ tuning of coupled superconducting microwave resonators. Rev. Sci. Inst. 87, 014707 (2016). 

J. Chang, E. Blackburn, O. Ivashko, A. T. Holmes, N. B. Christensen, M. Hucker, R. Liang, D. A. Bonn, W. N. Hardy, U. Rutt, M. von Zimmermann, E. M. Forgan, and S. M. Hayden, Magnetic field controlled charge density wave coupling in underdoped YBa₂Cu₃O_6+x. Nat. Communications 7, 11494 (2016). 

S. J. Kuhn, H. Kawano-Furukawa, E. Jellyman, R. Riyat, E. M. Forgan, M. Ono, K. Kihou, C. H. Lee, F. Hardy, P. Adelmann, T. Wolf, C. Meingast, J. Gavilano, M. R. Eskildsen, Simultaneous evidence for Pauli paramagnetic effects and multiband superconductivity in KFe₂As₂ by small-angle neutron scattering studies of the vortex lattice. Phys. Rev. B 93, 104527 (2016). 

A. K. R. Briffa, E. Blackburn, S. M. Hayden, E. A. Yelland, M. W. Long, and E. M. Forgan, Fermi surface reconstruction and quantum oscillations in underdoped YBa₂Cu₃O_7-x modeled in a single bilayer with mirror symmetry broken by charge density waves. Phys. Rev. B 93, 094502 (2016). 

L. S. Zhao, E. A. Yelland, J. A. N. Bruin, I. Sheikin, P. C. Canfield, V. Fritsch, H. Sakai, A. P. Mackenzie, and C. W. Hicks, Field-temperature phase diagram and entropy landscape of CeAuSb₂. Phys. Rev. B 93, 195124 (2016). 

2015 

M. Jeong and H. M. Rønnow, Quantum critical scaling for a Heisnberg spin-1/2 chain around saturation. Phys. Rev. B 92, 180409(R) (2015). 

H. Ishikawa, M. Yoshida, K. Nawa, M. Jeong, S. Krämer, M. Horvatić, C. Berthier, M. Takigawa, M. Akaki, A. Miyake, M. Tokunaga, K. Kindo, J. Yamaura, Y. Okamoto, and Z. Hiroi, One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite. Phys. Rev. Lett. 114, 227202 (2015). 

S. Babuin, E. Varga, W. F. Vinen, and L. Skrbek, Quantum turbulence of bellows-driven He-4 superflod: Decay. Phys. Rev. B 92, 184503 (2015). 

D. E. Zmeev, P. M. Walmsley, A. I. Golov, P. V. E. McClintock, S. N. Fisher, and W. F. Vinen, Dissipation of Quasiclassical Turbulence in Superfluid He-4. Phys. Rev. Lett. 115, 155303 (2015). 

A. Marakov, J. Gao, W. Guo, S. W. Van Scriver, G. G. Ihas, D. N. McKinsey, and W. F. Vinen, Visualization of the normal-fluid turbulence in counterflowing superfluid He-4. Phys. Rev. B 91, 094503 (2015). 

J. Gao, A. Marakov, W. Guo, B. T. Pawlowski, S. W. Van Sciver, G. G. Ihas, D. N. McKinsey, and W. F. Vinen, Producing and imaging a thin line of He-2* molecular tracers in helium-4. Rev. Sci. Inst. 86, 093904 (2015). 

E. M. Forgan, E. Blackburn, A. T. Holmes, A. K. R. Briffa, J. Chang, L. Bouchenoire, S. D. Brown, R. X. Liang, D. A. Bonn, W. N. Hardy, N. B. Christensen, M. von Zimmermann, M. Hucker, and S. M. Hayden, The microscopic structure of charge density waves in underdoped YBa₂Cu₃O_6.54 revealed by X-ray diffraction. Nat. Communications 6, 10064 (2015). 

N. G. Leos, J. S. White, J. A. Lim, J. L. Gavilano, B. Delley, L. Lemberger, A. T. Holmes, M. Medarde, T. Loew, V. Hinkov, C. T. Lin, M. Laver, C. D. Dewhurst, and E. M. Forgan, Influecne of the Fermi surface morphology on the magnetic field-driven vortex lattice structure transitions in YBa₂Cu₃O_7-d: d=0, 0.15. J. Phys. Soc. Japan 84, 044709 (2015). 

C. Lester, S. Ramos, R. S. Perry, T. P. Croft, R. I. Bewley, T. Guidi, P. Manuel, D. D. Khalyavin, E. M. Forgan, and S. M. Hayden, Field-tunable spin-density-wave phases in Sr₃Ru₂O₇. Nat. Materials 14, 373 (2015). 

C. W. Hicks, A. S. Gibbs, L. S. Zhao, P. Kushwaha, H. Borrmann, A. P. Mackenzie, H. Takatsu, S. Yonezawa, Y. Maeno, and E. A. Yelland, Quantum oscillations and magnetic reconstruction in the delafossite PdCrO₂. Phys. Rev. B 92, 014425 (2015). 

2014 

W. F. Vinen, Quantum Turbulence: Aspects of visualization and homogeneous turbulence. J. Low Temp. Physics 175, 305 (2014). 

R. Morisaki-Ishii, H. Kawano-Furukawa, A. S. Cameron, L. Lemberger, E. Blackburn, A. T. Holmes, E. M. Forgan, L. M. DeBeer-Schmitt, K. Littrell, M. Nakajima, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, S. Uchida, J. S. White, C. D. Dewhurst, J. L. Gavilano, and M. Zolliker, Vortex lattice structure in BaFe₂(As_0.67P_0.33)₂ via small-angle neutron scattering. Phys. Rev. B 90, 125116 (2014). 

M. Hucker, N. B. Christensen, A. T. Holmes, E. Blackburn, E. M. Forgan, R. X. Liang, D. A. Bonn, W. N. Hardy, O. Gutowski, M. von Zimmermann, S. M. Hayden, and J. Chang, Competing charge, spin, and superconducting orders in underdoped YBa₂Cu₃O_y. Phys. Rev. B 90, 054514 (2014). 

A. S. Cameron, J. S. White, A. T. Holmes, E. Blackburn, E. M. Forgan, R. Riyat, T. Loew, C. D. Dewhurst, and A. Erb, High magnetic field studies of the vortex lattice structure in YBa₂Cu₃O₇. Phys. Rev. B 90, 054502 (2014). 

C. W. Hicks, D. O. Brodsky, E. A. Yelland, A. S. Gibbs, J. A. N. Bruin, M. E. Barber, S. D. Edkins, K. Nishimura, S. Yonezawa, Y. Maeno, and A. P. Mackenzie, Strong increase of T_c of Sr₂RuO₄ under both tensile and compressive strain. Science 344, 283 (2014). 

C. W. Hicks, M. E. Barber, S. D. Edkins, D. O. Brodsky, and A. P. Mackenzie, Piezoelectric-based apparatus for strain tuning. Rev. Sci. Inst. 85, 065003 (2014). 

J. S. White, C. J. Bowell, A. S. Cameron, R. W. Heslop, J. Mesot, J. L. Gavilano, S. Strassle, L. Machler, R. Khasanov, C. D. Dewhurst, J. Karpinski, and E. M. Forgan, Magnetic field dependence of the basal-plane superconducting anisotropy in YBa₂Cu₄O₈ from small-angle neutron scattering measurements of the vortex lattice. Phys. Rev. B 89, 024501 (2014). 

2013 

M. Jeong, H. Mayaffre, C. Berthier, D. Schmidiger, A. Zheludev, and M. Horvatić, Attractive Tomonaga-Luttinger Liquid in a Quantum Spin Ladder. Phys. Rev. Lett. 111, 106404 (2013). 

Y. Mineda, M. Tsuobota, and W. F. Vinen, Decay of counterflow quantum turbulence in superfluid He-4. J. Low Temp. Physics 171, 511 (2013). 

Y. Mineda, M. Tsubota, Y. A. Sergeev, C. F. Barenghi, and W. F. Vinen, Velocity distributions of tracer particles in thermal counterflow in superfluid He-4. Phys. Rev. B 87, 174508 (2013). 

D. E. Zmeev, F. Papkour, P. M. Walmsley, A. I. Golov, P. V. E. McClintock, S. N. Fisher, W. Guo, D. N. McKinsey, G. G. Ihas, and W. F. Vinen, Observation of crossover from ballistic to diffusion regime for excimer molecules in superfluid He-4. J. Low Temp. Physics 171, 207 (2013). 

D. E. Zmeev, F. Papkour, P. M. Walmsley, A. I. Golov, W. Guo, D. N. McKinsey, G. G. Ihas, P. V. E. McClintock, S. N. Fisher, and W. F. Vinen, Excimers He-2* as tracers of quantum turbulence in He-4 in the T=0 limit. Phys. Rev. Lett. 110, 175303 (2013). 

H. Kawano-Furukawa, L. DeBeer-Schmitt, H. Kikuchi, A. S. Cameron, A. T. Holmes, R. W. Heslop, E. M. Forgan, J. S. White, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, T. Saito, H. Fukazawa, Y. Kohori, and J. L. Gavilano, Probing the anisotropic vortex lattice in the Fe-based superconductor KFe₂As₂ using small-angle neutron scattering. Phys. Rev. B 88, 134524 (2013). 

J. P. Bick, K. Suzuki, E. P. Gilbert, E. M. Forgan, R. Schweins, P. Lindner, C. Kubel, and A. Michels, Exchange-stiffness constant of a Nd-Fe-B based nanocomposite determined by magnetic neutron scattering. Appl. Phys. Lett. 103, 122402 (2013). 

E. Blackburn, J. Chang, A. H. Said, B. M. Leu, R. X. Liang, D. A. Bonn, W. N. Hardy, E. M. Forgan, and S. M. Hayden, Inelastic x-ray study of phonon broadening and charge-density wave formation in ortho-II-ordered Yba₂Cu₃O_6.54. Phys. Rev. B 88, 054506 (2013). 

F. M. Piegsa, M. Karlsson, B. van den Brandt, C. J. Carlile, E. M. Forgan, P. Hautle, J. A. Konter, G. J. McIntyre, and O. Zimmer, Polarized neutron Laue diffraction on a crystal containing dynamically polarized proton spins. J. Appl. Crystallography 46, 30 (2013). 

J. P. Bick, D. Honecker, F. Dobrich, K. Suzuki, E. P. Gilbert, H. Frielinghaus, J. Kohlbrecher, J. Gavilano, E. M. Forgan, R. Schweins, P. Lindner, R. Birringer, A. Micels, Magnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering. Appl. Phys. Lett. 102, 022415 (2013).