Observation of multilayer quantum Hall effect in the charge density wave material CaCu4As2

Subtle lattice distortion-driven phase transitions in layered ACu4As2 (A = Eu, Sr)

“…In both EuAg 4 As 2 and EuCu 4 As 2 , this transition is attributed to the structural distortion. Furthermore, for CaCu 4 As 2 , [22] a kink at ∼ 50 K with a hysteresis on ρ xx -T is identified as a result of CDW transition. In our samples, the λ -type anomalous hump of heat capacity near T P indicates that the T P -transition belongs to the second order-like thermodynamic phase transition.…”

Linear magnetoresistance and structural distortion in layered SrCu4–x P2 single crystals

“…4(a), the temperature-dependent resistivity ρ xx presents a small hysteresis between the cooling and heating cycles. Such a kink on ρ xx -T curves has been observed in EuAg 4 As 2 [6] and CaCu 4 As 2 , [15] which has been attributed to the structural distortion or charge density wave (CDW). In the following, we will focus on this transition, together with specific heat, thermal expansion and TEM analysis.…”

“…[16] For example, in the layered magnetic compound EuAg 4 As 2 , a phase transition was observed at 120 K, and incommensurate noncollinear long-range antiferromagnetism developed below 9 K. [6] In CaCu 4 As 2 , multilayer quantum Hall effects and phase transition below 51 K were observed. [15] Meanwhile, in recently reported EuCu 4 As 2 , both a large negative magnetoresistance (−55%, at 35 K, 9 T) near the magnetic transition temperature and a large positive magnetoresistance (60% at 2 K, 9 T) at lower temperatures were observed. [4] As a result of these observations, the investigation of other members of the CaCu 4 P 2 family may help to explore more exotic phenomena that contribute to this area.…”

“…In the past, a number of materials with rhombohedral CaCu 4 P 2 -type structures [1] have been synthesized, including the arsenides ACu 4 As 2 (A = Na, K, Ca, Sr, Ba, Eu) [2][3][4][5] and AAg 4 As 2 (A = Sr, Eu), [6][7][8][9] the antimonides ACu 4 Sb 2 (A = Na, K), [10] and the phosphides ACu 4−x P 2 (A = Ca, Sr, Ba, Y, La-Nd, Eu-Yb). [11][12][13] These compounds exhibit complex interplay between different orders, such as the coexistence, competition, and/or correlation of magnetism, [6,7,14] charge density waves, [15] and structural phase transitions. [16] For example, in the layered magnetic compound EuAg 4 As 2 , a phase transition was observed at 120 K, and incommensurate noncollinear long-range antiferromagnetism developed below 9 K. [6] In CaCu 4 As 2 , multilayer quantum Hall effects and phase transition below 51 K were observed.…”