Abstract
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 CsV
3
Sb
5
observed via second-harmonic generation under an in-plane magnetic field. The eMChA signal becomes significant only at temperatures below
$${T}^{{\prime} }\approx $$
T
′
≈
35 K, deep within the charge-ordered state of CsV
3
Sb
5
(
T
CDW
≈ 94 K). This temperature dependence reveals a direct correspondence between electronic chirality, unidirectional charge order
7
and spontaneous time-reversal symmetry breaking due to putative orbital loop currents
8–10
. 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. CsV
3
Sb
5
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.
Thermal conductance measurements are sensitive to both charge and chargeless energy flow and are an essential measurement technique in condensed-matter physics. For two-dimensional topological ...insulators, the determination of thermal Hall (transverse) conductance and thermal longitudinal conductance is crucial for the understanding of topological order in the underlying state. Such measurements have not been accomplished, even in the extensively studied quantum Hall effect regime. Here we report a local power measurement technique that we use to reveal the topological thermal Hall conductance, going beyond the ubiquitous two-terminal conductance. For example, we show that the thermal Hall conductance is approximately zero in the v = 2/3 particle–hole conjugated state. This is in contrast to the two-terminal thermal conductance that gives a non-universal value that depends on the extent of thermal equilibration between the counter-propagating edge modes. Moreover, we demonstrate the utility of this technique in studying the power carried by the current fluctuations of a partitioned edge mode with an out-of-equilibrium distribution.Careful thermal transport measurements identify the topological nature of transverse thermal conductance in the fractional quantum Hall regime.
Studies of energy flow in quantum systems complement the information provided by common conductance measurements. The quantum limit of heat flow in one-dimensional ballistic modes was predicted, and ...experimentally demonstrated, to have a universal value for bosons, fermions, and fractionally charged anyons. A fraction of this value is expected in non-Abelian states; harboring counterpropagating edge modes. In such exotic states, thermal-energy relaxation along the edge is expected, and can shed light on their topological nature. Here, we introduce a novel experimental setup that enables a direct observation of thermal-energy relaxation in chiral 1D edge modes in the quantum Hall effect. Edge modes, emanating from a heated reservoir, are partitioned by a quantum point contact (QPC) constriction, which is located at some distance along their path. The resulting low frequency noise, measured downstream, allows determination of the "effective temperature" of the edge mode at the location of the QPC. An expected, prominent energy relaxation was found in hole-conjugate states. However, relaxation was also observed in particlelike states, where heat is expected to be conserved. We developed a model, consisting of distance-dependent energy loss, which agrees with the observations; however, we cannot exclude energy redistribution mechanisms, which are not accompanied with energy loss.
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 CsV
Sb
observed via second-harmonic generation under an in-plane magnetic field. The eMChA signal becomes significant only at temperatures below Formula: see text 35 K, deep within the charge-ordered state of CsV
Sb
(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. CsV
Sb
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.
Thermal conductance measurements, sensitive to charge and chargeless energy flow, are evolving as an essential measurement technique in Condensed Matter Physics. For two-dimensional topological ...insulators, the measurements of the thermal Hall conductance, \(\kappa_{xy}T\), and the longitudinal one \(\kappa_{xx}T\), are crucial for the understanding of their underlying topological order. Such measurements are thus far lacking, even in the extensively studied quantum Hall effect (QHE) regime. Here, we report a new local power measurement technique that reveals the topological thermal Hall conductance (not the ubiquitous two-terminal one). For example, we find \(\kappa_{xy}\sim0\) of the challenging \(\nu=2/3\) particle-hole conjugated state. This is in contrast to the two-terminal measurement, which provides a non-universal value that depends on the extent of thermal equilibration between the counter-propagating edge modes. Moreover, we use this technique to study the power carried by the current fluctuations in a partitioned edge mode with an out-of-equilibrium distribution.
Studies of energy flow in quantum systems complement the information provided by common conductance measurements. The quantum limit of heat flow in one dimensional (1D) ballistic modes was predicted, ...and experimentally demonstrated, to have a universal value for bosons, fermions, and fractionally charged anyons. A fraction of this value is expected in non-abelian states. Nevertheless, open questions about energy relaxation along the propagation length in 1D modes remain. Here, we introduce a novel experimental setup that measures the energy relaxation in chiral 1D modes of the quantum Hall effect (QHE). Edge modes, emanating from a heated reservoir, are partitioned by a quantum point contact (QPC) located at their path. The resulting noise allows a determination of the 'effective temperature' at the location of the QPC. We found energy relaxation in all the tested QHE states, being integers or fractional. However, the relaxation was found to be mild in particle-like states, and prominent in hole-conjugate states.
Nature 611, 461 (2022) 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 magneto-chiral anisotropy
(eMChA). While chiral transport signatures are by symmetry allowed in many
conductors without a center of inversion, it reaches appreciable levels only in
rare cases when 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 centro-symmetric layered
Kagome metal CsV$_3$Sb$_5$, observed via second harmonic generation under
in-plane magnetic field. The eMChA signal becomes significant only at
temperatures below $T'\sim$ 35 K, deep within the charge-ordered state of
CsV$_3$Sb$_5$ ($T_{\mathrm{CDW}}\sim$ 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. CsV$_3$Sb$_5$ 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 -- a
prerequisite for their applications in chiral electronics.
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 ...magneto-chiral anisotropy (eMChA). While chiral transport signatures are by symmetry allowed in many conductors without a center of inversion, it reaches appreciable levels only in rare cases when 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 centro-symmetric layered Kagome metal CsV\(_3\)Sb\(_5\), observed via second harmonic generation under in-plane magnetic field. The eMChA signal becomes significant only at temperatures below \(T'\sim\) 35 K, deep within the charge-ordered state of CsV\(_3\)Sb\(_5\) (\(T_{\mathrm{CDW}}\sim\) 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. CsV\(_3\)Sb\(_5\) 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 -- a prerequisite for their applications in chiral electronics.
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