Near-field infrared spectroscopy of monolayer MnPS3

Abstract

We measured the near-field infrared response of MnPS3 in bulk, few-, and single-layer form and compared our findings with traditional far field vibrational spectroscopies, a symmetry analysis, and first principles lattice dynamics calculations. Trends in the Bu mode near 450 cm −1 are striking, with the disappearance of this structure in the thinnest sheets. Combined with the amplified response of the activated Ag mode and analysis of the Au + Bu features, we find that symmetry is unexpectedly increased in few-and single-sheet MnPS3 due to a restoration of the threefold axes of rotation. Monoclinicity in this system is therefore a consequence of the long-range stacking pattern and temperature rather than local structure.

Synchrotron infrared nano-spectroscopy and -imaging

“…The sensitivity of SINS is high enough to discriminate, e.g., small changes in the local free carrier concentration associated with defects, doping, impurities, and layer thickness. [111,112] In an example combining optical, X-ray, and electron probes, SINS was used to investigate the electronic heterogeneities in topological insulator (TI) and thermoelectric materials Bi2Se3 and Sb2Te3 in a multimodal atomic-to-mesoscale resolution imaging study. [113] From the broadband SINS spectra and subsequent modeling of the tip-sample scattering response, the Drude free carrier concentration was extracted from several locations of the heterogeneous optical response in TI nanocrystals.…”

Exploring few and single layer CrPS4 with near-field infrared spectroscopy

“…Repeated measurements were conducted to confirm stability over the measurement period. AFM mapping to identify an ideal measurement area, as well as sheet thickness studies was completed as described in prior work [20,22].…”

“…These systems are attracting particular attention (1) as candidate multiferroics [3], (2) for their tunability under external stimuli such as pressure, magnetic field, and temperature [4][5][6][7][8][9][10][11], (3) for their ease of exfoliation [12][13][14][15][16], and (4) as platforms for studying magnetism in the ultrathin limit [10,12,[17][18][19][20][21][22]. Monolayers of MnPS 3 , FePS 3 , and NiPS 3 display quite different functionalities including magnetism, electron-phonon coupling, and symmetry breaking [10,12,[17][18][19][20]22]. Extension to related members of the series including CrPS 4 and CuInP 2 S 6 will enhance our understanding of these properties and, at the same time, allow for the development of structure-property relations.…”

“…In order to extend recent spectroscopic studies of complex chalcogenides [20,22], we measured the near-field infrared response of CrPS 4 in bulk, few-, and single-layer form. We compare our findings with complementary lattice dynamics calculations as well as prior work on the MPS 3 family of materials (M = Mn, Fe, Ni) revealing surprising differences in symmetry behavior stemming, in part, from the lack of a phosphorus-phosphorus dimer in CrPS 4 .…”

Spin photogalvanic effect in two-dimensional collinear antiferromagnets

“…The magnetic moments of the nearest-neighbor Mn atoms are antiparallel to each other, forming a Néel-type AFM order. It has been successfully exfoliated down to single-layer recently 7,8,[41][42][43] , and the Néel-type AFM order can be maintained. The magnetic sublattices in monolayer MnPS 3 have the noncentrosymmetric structure with D 3 point group, which contains a C 3 rotation symmetry along the z-axis, and a C 2 rotation axis around the y direction, as shown in Fig.…”