Quasi-Two-Dimensional Heterostructures (KM_1 – xTe)(LaTe₃) (M = Mn and Zn) with Charge Density Waves

Abstract

Layered heterostructure materials with two different functional building blocks can teach us about emergent physical properties and phenomena arising from interactions between the layers. We report intergrowth compounds KLaM 1 − x Te 4 (M = Mn and Zn; x ≈ 0.35) featuring two chemically distinct alternating layers [LaTe 3 ] and [KM 1 − x Te]. Their crystal structures are incommensurate, determined by single X-ray diffraction for the Mn compound and a transmission electron microscope study for the Zn compound. KLaMn 1 − x Te 4 crystallizes in the orthorhombic superspace group Pmnm(01/2γ)s00 with lattice parameters a = 4.4815(3) Å, b = 21.6649(16) Å, and c = 4.5220(3) Å. It exhibits charge density wave order at room temperature with a modulation wave vector q = 1/2b* + 0.3478c* originating from electronic instability of Te-square nets in [LaTe 3 ] layers. The Mn analog exhibits a cluster spin glass behavior with spin freezing temperature T f ≈ 5 K attributed to disordered Mn vacancies and competing magnetic interactions in the [Mn 1 − x Te] layers. The Zn analog also has charge density wave order at room temperature with a similar q-vector having the c* component ∼0.346 confirmed by selected-area electron diffraction. Electron transfer from [KM 1 − x Te] to [LaTe 3 ] layers exists in KLaM 1 − x Te 4 , leading to an enhanced electronic specific heat coefficient. The resistivities of KLaM 1 − x Te 4 (M = Mn and Zn) exhibit metallic behavior at high temperatures and an upturn at low temperatures, suggesting partial localization of carriers in the [LaTe 3 ] layers with some degree of disorder associated with the M atom vacancies in the [M 1 − x Te] layers.

Spontaneous interlayer compression in commensurately stacked van der Waals heterostructures

“…This is the case for our Ti-based heterostructures as well: There is a net charge transfer between the layers and both layers become doped as shown in Table III (this doping must be reciprocal as the full system is charge neutral). Stabilization via charge transfer is also thought to occur in non-TMD layered materials [21].…”

“…At the two lowest modes are polar in-plane displacements of the Ti against S, i.e., ferroelectric. Given the experimental demonstration of CDW suppression in heterostructures [21], it would be very interesting if this behavior could be confirmed experimentally as well: 2D ferroelectrics are highly sought after for ultrathin and flexible sensors, actuators, and memory devices. The phonon displacement vectors at M for the lowest imaginary mode are in-plane, with the two S atoms moving in opposite directions along a (110) high-symmetry axis.…”

“…Stacked heterostructures with different transition-metal dichalcogenides (TMDs) (e.g., MoSe 2 on WSe 2 ) have long-lived interlayer excitons, resulting in spatially separated electrons and holes [15,19,20], an ideal feature for photovoltaic applications. Stacking of non-TMD layered materials into incommensurate heterostructures has also been shown to lead to enhancements in the electronic specific heat of the heterostructure and stabilization of native charge density waves [21]. Low-frequency Raman measurements of heterostructure materials [22][23][24] can be used to determine the strength of layer interactions in a heterostructure lattice.…”

A Heavy Fermion Zn-Deficient CaBe2Ge2-Type Phase with Rare Ce-Based Ferromagnetism and Large Magnetoresistance

“…The discovery of new materials has proven time and time again to be a crucial stimulus for fundamental research and eventually technological progress. − For the discovery of new quantum materials with strongly correlated electrons, chemical design principles and exploratory chemical syntheses are essential for advancements in this field. − Especially the computation, e.g. , the implementation in density functional calculation, of electronic correlations remains a major challenge .…”