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AV3Sb5 general properties

Interesting Properties

Electronic Properties

Low temperature

AV3Sb5_Prop.png

  1. Well-defined Meissner effect can be seen in fig. 2(e)
  2. Sharp entropy anomaly at SC transition
  3. Small critical field,\(H_c = 0.4T\).
  4. All AV3Sb5 compounds within the material family are superconducting at low temperature.

Above SC temperature

  1. Normal states show quite different behavior.
  2. Typical metallic behavior modelled by \(\rho(T)=\rho_0 +aT^2\).
  3. Anomaly in temperature dependent electrical resistivity, and heat capacity (see fig.2(f, g)).
  4. Large anisotropy which agrees with V kagome layer playing a dominant role, confirming Quasi 2D Material nature.

Important

The kink behaviorin the \(\rho(T)\) variation around 94K is related to long range CDW order. The sharp peak in heat capacity indicates the CDW transition is First order Phase transition

CDW

  1. CDW phase occurs for all the members of AV3Sb5 family.
  2. No long range order. (Neutron scattering measurements and Muon spin spectroscopy)
  3. Transition derives from charge Degree of freedom.
  4. The transition is a CDW transition with \(2 \times 2\) superlattice modulation.
  5. Energy gap opening around the Fermi level of \(\sim 50 meV\) which together with \(2\times 2\) superlattice modulation disappears above \(T_{CDW}\)
  6. Charge reversal across this gap. Hallmark of CDW ordering.
  7. ARPES measurements on KV3Sb5 suggest the importance of structural transition.

Time reversal symmetry

  1. Symmetry breaking signals was found in the CDW phases of \(AV_3Sb_5\) compounds.
  2. There are six CDW ordering vectors \(Q_{3Q}\) from the STM topographic spectrum.
  3. However, the intensity of these three pairs of vectors are different in the clean regions for all \(AV_3Sb_5\) materials.
  4. This defines the Chirality of the CDW order.(direction from the lowest intensity peaks to the highest)
  5. This chirality shows an unusual response to the perturbation of the external MF.

KV3Sb5_CDW_MF.png The highest vector peaks shift their positions under magnetic field applied along c-axis

  1. Onsager reciprocal relation, the response functions of a time-reversal preserving system under +B and -B must relate to each other by a time reversal operator. This non-reciprocal relation under magnetic field breaks the Onsager relation, indicating the Time reversal symmetry in this non-magnetic kagome system (Kagome metal).
  2. Emergence of local MF under \(T_{CDF}\) due to Time reversal symmetry.
  3. Giant Anomalous Hall effect has also been observed in \(AV_3Sb_5\) with onset concurrent with CDW order. (Usual causes are intrinsic Berry curvature and extrinsic impurity scattering)
  4. Slightly unconventional Anomalous Hall effect is observed.
  5. It exhibits \(\sigma_{AHE}(B\rightarrow 0) = 0\) without Hysteresis behavior.

Inversion symmetry

  1. Inversion symmetry remains a valid symmetry for \(AV_3Sb_5\) at all temperatures.
  2. This constrains the CDW order and is important for superconducting pairing possibilities.
  3. Nematicity

Important

\(AV_3Sb_5\) has structural Instability which can lead to two different types of configuration Star of David and Tri-Hexagonal as discussed in CsV3Sb5 DFT. Recent studies show that the average structure shows signatures of both TrH and SoD structures in staggered layer sequence.

Related Links AV3Sb5 anomalies