A Natural 2D Heterostructure [Pb_3.1Sb_0.9S₄][Au_xTe_2–x] with Large Transverse Nonsaturating Negative Magnetoresistance and High Electron Mobility

Abstract

We report the two-dimensional (2D) natural heterostructure [Pb3.1Sb0.9S4][AuxTe2-x] (x = 0.52 − 0.36) which shows anomalous, transverse nonsaturating negative magnetoresistance (MR). For x = 0.52, the material has a commensurately modulated structure with alternating [Pb3.1Sb0.9S4] rocksalt layers and atomically thin [AuxTe2-x] sheets, as determined by single crystal X-ray diffraction using a (3 + 1)-dimensional space group; for other x compositions, the modulated structures are absent and the Au and Te atoms are disordered. The transport properties in this system in low temperature (< 100 K) are dominated by an unusual 2D hopping mechanism, while at room temperature a high carrier mobility of ~1352 cm 2 V-1 s-1 is obtained (x = 0.36). The confined electrons within the [AuxTe2-x] layers are also exposed to inter-layer coupling with the insulating [Pb3.1Sb0.9S4] layers and as a result the properties of the heterostructures emerge not only from the constituent layers, but also the interactions between them. Furthermore, the various Au and Te coordination patterns found in the [AuxTe2-x] sheets as a function of x further contribute to a unique electronic structure that leads to the anomalous non-saturating negative MR with different field dependent behaviors. First-principles calculations indicate that the [AuxTe2-x] sheets are responsible for the unusual electrical transport properties in this 2D system.

Naturally Occurring 2D Heterostructure Nagyágite with Anisotropic Optical Properties

“…Therefore, the lattice parameters in the a–b plane are , , and γ = 90.6° for the current natural nagyágite crystal, which are more or less close to the previously determined lattice parameters of , , and γ = 90° for one synthetic nagyágite crystal, [ 27 ] as well as , , and γ = 90° for another synthetic nagyágite. [ 26 ] The selected area electron diffraction (SAED) pattern along the surface normal to the [001] crystal zone axis is shown in Figure 1k. It should be noted that due to the commensuration between the constituent lattices of the nagyágite crystal, the generated spot patterns from individual layers are identical.…”

“…A previous study on synthetic nagyágite revealed that it has high electron mobility and hence a very narrow band gap. [ 26 ] Low‐temperature resistivity measurement revealed that the resistivity of the material increases with decreasing temperature, indicating semiconducting behavior. However, no obvious band gap above 0.05 eV was observed even in electronic absorption spectroscopy, due to the interference from free carriers in nagyágite.…”

“…Recently, synthetic nagyágite crystals with a thickness of 50 µm have been reported to show high room‐temperature electron mobility and large transverse nonsaturating negative magnetoresistance. [ 26 ] However, as a layered mineral, till‐date there has been no study on the exfoliation of naturally occurring nagyágite crystals. Also, as a monoclinic layered crystal, the anisotropic optical properties of nagyágite have not been studied yet.…”

Covalent Chemistry on a Van Der Waals Heterostructure

“…24 Alternatively, one can obtain ultrathin van der Waals heterostructures from the direct exfoliation of minerals of adequate composition. [20][21][22][23][25][26][27][28] The motivation behind this field of research is based on the expectation that the combination (or modulation) of properties of nanomaterials is a promising approach towards materials by design. [11][12][13][14][15][16][17] This exact same motivation fuels the interest in the chemistry of 2D materials: 8,9 we expect that the decoration of the nanomaterials with functional molecular fragments will yield superior combined properties.…”

Covalent Chemistry on a Van Der Waals Heterostructure

“…24 Alternatively, one can obtain ultrathin van der Waals heterostructures from the direct exfoliation of minerals of adequate composition. [20][21][22][23][25][26][27][28] The motivation behind this field of research is based on the expectation that the combination (or modulation) of properties of nanomaterials is a promising approach towards materials by design. [11][12][13][14][15][16][17] This exact same motivation fuels the interest in the chemistry of 2D materials: 8,9 we expect that the decoration of the nanomaterials with functional molecular fragments will yield superior combined properties.…”