32 research outputs found
Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor
Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc
Directional ballistic transport in the two-dimensional metal PdCoO2
In an idealized infinite crystal, the material properties are constrained by
the symmetries of its unit cell. Naturally, the point-group symmetry is broken
by the sample shape of any finite crystal, yet this is commonly unobservable in
macroscopic metals. To sense the shape-induced symmetry lowering in such
metals, long-lived bulk states originating from anisotropic Fermi surfaces are
needed. Here we show how strongly facetted Fermi surfaces and long
quasiparticle mean free paths present in microstructures of PdCoO2 yield an
in-plane resistivity anisotropy that is forbidden by symmetry on an infinite
hexagonal lattice. Bar shaped transport devices narrower than the mean free
path are carved from single crystals using focused ion beam (FIB) milling, such
that the ballistic charge carriers at low temperatures frequently collide with
both sidewalls defining a channel. Two symmetry-forbidden transport signatures
appear: the in-plane resistivity anisotropy exceeds a factor of 2, and
transverse voltages appear in zero magnetic field. We robustly identify the
channel direction as the source of symmetry breaking via ballistic Monte- Carlo
simulations and numerical solution of the Boltzmann equation
Switchable chiral transport in charge-ordered kagome metal CsV3Sb5
When electric conductors differ from their mirror image, unusual chiral transport coefficients appear that are forbidden in achiral metals, such as a non-linear electric response known as electronic magnetochiral anisotropy (eMChA). Although chiral transport signatures are allowed by symmetry in many conductors without a centre of inversion, they reach appreciable levels only in rare cases in which an exceptionally strong chiral coupling to the itinerant electrons is present. So far, observations of chiral transport have been limited to materials in which the atomic positions strongly break mirror symmetries. Here, we report chiral transport in the centrosymmetric layered kagome metal CsVSb observed via second-harmonic generation under an in-plane magnetic field. The eMChA signal becomes significant only at temperatures below 35 K, deep within the charge-ordered state of CsVSb (T ≈ 94 K). This temperature dependence reveals a direct correspondence between electronic chirality, unidirectional charge order and spontaneous time-reversal symmetry breaking due to putative orbital loop currents. We show that the chirality is set by the out-of-plane field component and that a transition from left- to right-handed transport can be induced by changing the field sign. CsVSb is the first material in which strong chiral transport can be controlled and switched by small magnetic field changes, in stark contrast to structurally chiral materials, which is a prerequisite for applications in chiral electronics
Switchable chiral transport in charge-ordered kagome metal CsV3Sb5
When electric conductors differ from their mirror image, unusual chiral transport
coefficients appear that are forbidden in achiral metals, such as a non-linear electric
response known as electronic magnetochiral anisotropy (eMChA)1–6
. Although chiral
transport signatures are allowed by symmetry in many conductors without a centre of
inversion, they reach appreciable levels only in rare cases in which an exceptionally
strong chiral coupling to the itinerant electrons is present. So far, observations of
chiral transport have been limited to materials in which the atomic positions strongly
break mirror symmetries. Here, we report chiral transport in the centrosymmetric
layered kagome metal CsV3Sb5 observed via second-harmonic generation under an
in-plane magnetic field. The eMChA signal becomes significant only at temperatures
below T′≈ 35 K, deep within the charge-ordered state of CsV 3Sb5 (TCDW ≈ 94 K). This
temperature dependence reveals a direct correspondence between electronic
chirality, unidirectional charge order7 and spontaneous time-reversal symmetry
breaking due to putative orbital loop currents8–10
. We show that the chirality is set by
the out-of-plane field component and that a transition from left- to right-handed
transport can be induced by changing the field sign. CsV3Sb5 is the first material in
which strong chiral transport can be controlled and switched by small magnetic field
changes, in stark contrast to structurally chiral materials, which is a prerequisite for
applications in chiral electronics.This work was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (MiTopMat, grant agreement no. 715730, and PARATOP, grant agreement no. 757867). This project received funding by the Swiss National Science Foundation (grant no. PP00P2_176789). M.G.V., I.E. and M.G.-A. acknowledge the Spanish Ministerio de Ciencia e Innovacion (grant PID2019-109905GB-C21). M.G.V., C.F. and T.N. acknowledge support from FOR 5249 (QUAST) lead by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). This work has been supported in part by Basque Government grant IT979-16. This work was also supported by the European Research Council Advanced Grant (no. 742068) ‘TOPMAT’, the Deutsche Forschungsgemeinschaft (Project-ID no. 247310070) ‘SFB 1143’ and the DFG through the Würzburg–Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter ct.qmat (EXC 2147, Project-ID no. 390858490).
Open access funding provided by Max Planck Society
Distinct switching of chiral transport in the kagome metals KVSb and CsVSb
The kagome metals AVSb (A=K,Rb,Cs) present an ideal sandbox to study
the interrelation between multiple coexisting correlated phases such as charge
order and superconductivity. So far, no consensus on the microscopic nature of
these states has been reached as the proposals struggle to explain all their
exotic physical properties. Among these, field-switchable electric
magneto-chiral anisotropy (eMChA) in CsVSb provides intriguing evidence
for a rewindable electronic chirality, yet the other family members have not
been likewise investigated. Here, we present a comparative study of
magneto-chiral transport between CsVSb and KVSb. Despite their
similar electronic structure, KVSb displays negligible eMChA, if any,
and with no field switchability. This is in stark contrast to the
non-saturating eMChA in CsVSb even in high fields up to 35 T. In light
of their similar band structures, the stark difference in eMChA suggests its
origin in the correlated states. Clearly, the V kagome nets alone are not
sufficient to describe the physics and the interactions with their environment
are crucial in determining the nature of their low-temperature state