arXiv subjects

A. P. Mackenzie

Publications and source records attributed to A. P. Mackenzie.

At least 73 records · Page 4Linked to original sources

arXiv2008

Evidence for the Sr2RuO4 intercalations in the Sr3Ru2O7 region of the Sr3Ru2O7-Sr2RuO4 eutectic system

Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far, ac susceptibility measurements revealed multiple superconducting transitions occurring in the Sr3Ru2O7 region cut from Sr3Ru2O7-Sr2RuO4 eutectic crystals. Based on various experimental results, some of us proposed the scenario in which Sr2RuO4 thin slabs with a few layers of the RuO2 plane are embedded in the Sr3Ru2O7 region as stacking faults and multiple superconducting transitions arise from the distribution of the slab thickness. To examine this scenario, we measured the resistivity along the ab plane (rho_ab) using a Sr3Ru2O7-region sample cut from the eutectic crystal, as well as along the c axis (rho_c) using the same crystal. As a result, we detected resistance drops associated with superconductivity only in rho_ab, but not in rho_c. These results support the Sr2RuO4 thin-slab scenario. In addition, we measured the resistivity of a single crystal of pure Sr3Ru2O7 with very high quality and found that pure Sr3Ru2O7 does not exhibit superconductivity down to 15 mK.

cond-mat.supr-con↗

arXiv2008

Fermi surface and van Hove singularities in the itinerant metamagnet Sr3Ru2O7

The low-energy electronic structure of the itinerant metamagnet Sr3Ru2O7 is investigated by angle resolved photoemission and density functional calculations. We find well-defined quasiparticle bands with resolution limited line widths and Fermi velocities up to an order of magnitude lower than in single layer Sr2RuO4. The complete topography, the cyclotron masses and the orbital character of the Fermi surface are determined, in agreement with bulk sensitive de Haas - van Alphen measurements. An analysis of the dxy band dispersion reveals a complex density of states including van Hove singularities (vHs) near the Fermi level; a situation which is favorable for magnetic instabilities.

cond-mat.str-el↗

arXiv2008

De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe_3)

De Haas-van Alphen oscillations were measured in lanthanum tritelluride (LaTe_3) to probe the partially gapped Fermi surface resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state.

cond-mat.str-el↗

arXiv2006

Formation of a Nematic Fluid at High Fields in Sr3Ru2O7

In principle, a complex assembly of strongly interacting electrons can self-organise into a wide variety of collective states, but relatively few such states have been identified in practice. We report that, in the close vicinity of a metamagnetic quantum critical point, high purity Sr3Ru2O7 possesses a large magnetoresistive anisotropy, consistent with the existence of an electronic nematic fluid. We discuss a striking phenomenological similarity between our observations and those made in high purity two-dimensional electron fluids in GaAs devices.

cond-mat.str-el↗

arXiv2006

Anisotropic Scattering and Anomalous Transport in a High Temperature Superconductor

The metallic state of high temperature cuprate superconductors is markedly different from that of textbook metals. The origin of this unconventional state, characterized by unusual and distinct temperature dependences in the transport properties, remains unresolved despite intense theoretical efforts. Our understanding is impaired by our inability to determine experimentally the temperature and momentum dependence of the transport scattering rate. Here we use a novel magnetotransport probe to show that the unusual temperature dependences of the resistivity and the Hall coefficient in highly doped Tl$_2$Ba$_2$CuO$_{6+δ}$ originate from two distinct inelastic scattering channels. One channel is due to conventional electron-electron scattering whilst the other is highly anisotropic, has the same symmetry as the superconducting gap and a magnitude that grows approximately linearly with temperature. The observed form and anisotropy put tight constraints on theories of the metallic state. Moreover, in heavily doped non-superconducting cuprates, this anisotropic scattering term appears to be absent, suggesting an intimate connection between the origin of this scattering and superconductivity itself.

cond-mat.supr-con↗

arXiv2006

Thermal conductivity in the vicinity of the quantum critical endpoint in Sr3Ru2O7

Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic fields through the quantum critical endpoint at H_c = 7.85 T. A peak in the electrical resistivity as a function of field was mimicked by the thermal resistivity. In the limit as T -> 0 K we find that the Wiedemann-Franz law is satisfied to within 5% at all fields, implying that there is no breakdown of the electron despite the destruction of the Fermi liquid state at quantum criticality. A significant change in disorder (from $ρ_0$(H=0T) = 2.1 $μΩ$ cm to 0.5 $μΩ$ cm) does not influence our conclusions. At finite temperatures, the temperature dependence of the Lorenz number is consistent with ferromagnetic fluctuations causing the non-Fermi liquid behavior as one would expect at a metamagnetic quantum critical endpoint.

cond-mat.str-el↗

arXiv2006

Fermi surface and quasiparticle excitations of Sr$_{2}$RhO$_{4}$

The electronic structure of the layered 4$d$ transition metal oxide Sr$_{2}$RhO$_{4}$ is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi liquid like ground state. Markedly different from the isostructural Sr$_{2}$RuO$_{4}$, only two bands with dominant Rh 4$d_{xz,zy}$ character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.

cond-mat.str-el↗

arXiv2005

Phase Bifurcation and Quantum Fluctuations in Sr3Ru2O7

The bilayer ruthenate Sr_3Ru_2O_7 has been cited as a textbook example of itinerant metamagnetic quantum criticality. However, recent studies of the ultra-pure system have revealed striking anomalies in magnetism and transport in the vicinity of the quantum critical point. Drawing on new experimental data, we propose that the anomalous phase behavior can be accommodated by a mechanism which relies on the effects of strong magnetoelastic coupling. We argue that the phenomenological theory identified here is more generic and raises the possibility of quantum tricritical behaviour.

cond-mat.str-el↗

arXiv2004

Low-Temperature Hall Effect in Substituted Sr2RuO4

We report the results of a study of the Hall effect and magnetoresistance in single crystals of Sr2RuO4 in which Sr^(2+) has been substituted by La^(3+) (Sr(2-y)La(y)RuO(4)) or Ru^(4+) by Ti^(4+) (Sr(2)Ru(1-x)Ti(x)O(4)). For undoped Sr2RuO4, the purity is so high that the strong-field Hall coefficient can be measured for fields above 4 T. The conventional weak-field Hall coefficient as a function of doping shows a sharp jump and sign change at y ~ 0.01 that is unrelated to either a sharp change in Fermi-surface topography or a magnetic instability. The implications of these results are discussed.

cond-mat.str-el↗

arXiv2004

Band-Selective Modification of the Magnetic Fluctuations in Sr2RuO4: Study of Substitution Effects

We report a study of magnetic, thermal, and transport properties of La(3+) substituted Sr2RuO4, performed in order to investigate the effects of additional electron doping in this correlated metal. A gradual enhancement of the electronic part of specific heat and a more drastic increase of the static magnetic susceptibility were observed in Sr(2-y)La(y)RuO(4) with increasing y. Furthermore, the quasi-two-dimensional Fermi-liquid behavior seen in pure Sr2RuO4 breaks down near the critical concentration y ~ 0.20. Combined with a realistic tight-binding model with rigid-band shift of Fermi level, the enhancement of the density of states can be ascribed to the elevation of the Fermi energy toward a van Hove singularity of the thermodynamically dominant γFermi-surface sheet. On approaching the van Hove singularity, the effective nesting-vector of the γband shrinks and further enhances the susceptibility near the wave vector q ~ 0. We attribute the non-Fermi-liquid behavior to two-dimensional ferromagnetic fluctuations with short range correlations at the van Hove singularity. The observed behavior is in sharp contrast to that of Ti(4+) substitution in Sr2RuO4 which enhances antiferromagnetic fluctuations and subsequently induces incommensurate magnetic ordering associated with the nesting between the other Fermi-surface sheets (αand β). We thus establish that substitution of appropriate chemical dopants can band-selectively modify the spin-fluctuation spectrum in the spin-triplet superconductor Sr2RuO4.

cond-mat.str-el↗

arXiv2004

The de Haas-van Alphen effect across the metamagnetic transition in Sr$_3$Ru$_2$O$_7$

We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant metamagnet Sr$_3$Ru$_2$O$_7$. Extremely high sample purity allows the observation of dHvA oscillations both above and below the metamagnetic transition field of 7.9 T. The quasiparticle masses are fairly large away from the transition, and are enhanced by up to an extra factor of three as the transition is approached, but the Fermi surface topography change is quite small. The results are qualitatively consistent with a field-induced Stoner transition in which the mass enhancement is the result of critical fluctuations.

cond-mat.str-el↗

arXiv2004

Rigid-Band Shift of the Fermi Level in a Strongly Correlated Metal: Sr(2-y)La(y)RuO(4)

We report a systematic study of electron doping of Sr2RuO4 by non-isovalent substitution of La^(3+) for Sr^(2+). Using a combination of de Haas-van Alphen oscillations, specific heat, and resistivity measurements, we show that electron doping leads to a rigid-band shift of the Fermi level corresponding to one doped electron per La ion, with constant many-body quasiparticle mass enhancement over the band mass. The susceptibility spectrum is substantially altered and enhanced by the doping but this has surprisingly little effect on the strength of the unconventional superconducting pairing.

cond-mat.str-el↗

arXiv2004

Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure

We present measurements on ultra clean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetisation across the metamagnetic transition. Very near the metamagnetic field, unusual behaviour is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behaviour is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed. PACS: 68.35.Rh, 71.27.+a, 72.15.-v, 74.70.Pq

cond-mat.str-el↗

arXiv2003

Angular dependence of the magnetic susceptibility in the itinerant metamagnet Sr3Ru2O7

We report the results of a study of the di erential magnetic susceptibility of Sr3Ru2O7 as a function of temperature and magnetic elds applied at a series of angles to the ab plane. By analysing the real and imaginary parts of the susceptibility, we conclude that the eld angle acts as a continuous tuning parameter for the critical end-point to a line of rst order metamagnetic phase transitions. The end-point sits at approximately 1.25K for elds applied in the ab plane, and is depressed to below 50 mK when the eld is aligned within 10 of the c axis.

cond-mat.str-el↗

arXiv2002

Transport spin polarisation in SrRuO3 measured through Point Contact Andreev reflection

We report a study in which Andreev reflection using a Nb point contact is used to measure the transport spin polarisation of the 4d itinerant ferromagnet SrRuO3. By performing the study in high quality thin films with residual resistivities less than 7micro-ohm-cm, we ensure that the study is done in the ballistic limit, a regime which is difficult to reach in oxide ferromagnets. The degree of transport spin polarisation that we find is comparable to that of the hole doped rare-earth manganites. We conclude that the large transport spin polarisation results mainly from a difference in the Fermi velocities between the majority and minority spin channels in this material.

cond-mat.str-el↗

arXiv2002

Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and Pure d-wave BCS Superconductor

The transport of heat and charge in the overdoped cuprate superconductor Tl_2Ba_2CuO_(6+delta) was measured down to low temperature. In the normal state, obtained by applying a magnetic field greater than the upper critical field, the Wiedemann-Franz law is verified to hold perfectly. In the superconducting state, a large residual linear term is observed in the thermal conductivity, in quantitative agreement with BCS theory for a d-wave superconductor. This is compelling evidence that the electrons in overdoped cuprates form a Fermi liquid, with no indication of spin-charge separation.

cond-mat.supr-con↗

arXiv2002

Critical end-point and metamagnetic quantum criticality in Sr3Ru2O7

We report a metamagnetic critical point at (B*,T*)=(5.1T,1.1K) for magnetic fields applied perpendicular to the (tetragonal) c-axis of Sr3Ru2O7. First-order behaviour well below T* indicates that (B*,T*) marks a critical end-point that terminates a line of first-order metamagnetic transitions. The absence of first-order behaviour in the metamagnetic transition with B||c confirms that the non-Fermi liquid behaviour for B||c is underpinned by a metamagnetic quantum critical end-point for which T*->0. Scaling behaviour of the resistivity under hydrostatic pressure yields the surprising result that although B* increases rapidly with pressure, T* has only a weak pressure dependence.

cond-mat.str-el↗

arXiv2002

Observation of Two-dimensional Spin Fluctuations in the Bilayer Ruthenate Sr3Ru2O7 by Inelastic Neutron Scattering

We report the first observation of two-dimensional incommensurate magnetic fluctuations in the layered metallic perovskite Sr3Ru2O7. The wavevectors where the magnetic fluctuations are strongest are different from those observed in the superconducting single layer ruthenate Sr2RuO4 and appear to be determined by Fermi surface nesting. No antiferromagnetic ordering is observed for temperatures down to 1.5K. For temperatures T<20K, the fluctuations become predominately ferromagnetic. Our inelastic neutron scattering measurements provide concrete evidence of the coexistence of competing interactions in Sr3Ru2O7 and of the low energy scale of the fluctuations.

cond-mat.str-el↗