Determining the phase diagram of atomically thin layered antiferromagnet CrCl3

Abstract

Changes in the spin configuration of atomicallythin, magnetic van-der-Waals multilayers can cause drastic modifications in their optoelectronic properties.Conversely, the optoelectronic response of these systems provides information about the magnetic state, very difficult to obtain otherwise. Here we show that in CrCl 3 multilayers, the dependence of the tunnelling conductance on applied magnetic field (H), temperature (T ), and number of layers (N ) tracks the evolution of the magnetic state, enabling the magnetic phase diagram of these systems to be determined experimentally. Besides a high-field spinflip transition occurring for all thicknesses, the inplane magnetoconductance exhibits an even-odd effect due to a low-field spin-flop transition. If the layer number N is even, the transition occurs at µ 0 H ∼ 0 T due to the very small in-plane magnetic anisotropy, whereas for odd N the net magnetization of the uncompensated layer causes the transition to occur at finite H. Through a quantitative analysis of the phenomena, we determine the interlayer exchange coupling as well as the staggered magnetization, and show that in CrCl 3 shape anisotropy dominates. Our results reveal the rich behaviour of atomically-thin layered antiferromagnets with weak magnetic anisotropy.The recent discovery of magnetism in atomically thin layers exfoliated from bulk van der Waals (vdW) crystals is a major breakthrough 1-13 , with important implications in the field of two-dimensional (2D) materials and heterostructures [14][15][16] . The observation of a giant tunnelling magnetoresistance through CrI 3 multilayers 17-20 , for instance, makes clear that semiconducting vdW antiferromagnets are very interesting systems 21-23 , with potential relevance for technology 24,25 once room-temperature operation is achieved. It is therefore important to identify the microscopic parameters governing the behaviour of these systems, and to understand how they can be determined experimentally. In CrI 3 , the observed phenomenology originates from transitions in which the magnetization of individual layers abruptly flips direction under the application of a perpendicular magnetic field 17-20 (H), as expected when the uniaxial magnetic anisotropy is the dominating energy scale 26,27 . The case of weak anisotropy is different, as a richer variety of magnetic transitions is predicted to occur at lower field 27,28 , and indeed in bulk vdW layered antiferromagnets the occurrence of spin-flop phases 29 is well established 30 . However, the phase diagram of weakly anisotropic atomically-thin vdW layered antiferromagnets, where finite-size effects can give rise to new phenomena 31-34 , has not been determined yet.Here, we investigate atomically thin multilayers of CrCl 3 , a layered vdW antiferromagnetic semiconductor with a small anisotropy that favours spins to lie in the plane of the layers 35-39 ( Fig. 1a; see Supplementary Notes 1-2 and Figures 1-2). We show that the extreme sensitivity of the tunnelling current to the magnetic state can be exploited ...

Luminescent Emission of Excited Rydberg Excitons from Monolayer WSe2

“…Single electron transistor spectroscopy has found both electron and hole masses to be about 0.4-0.6 0 40 . In a magneto-optical measurement study of the inter-Landau level transition 41 , the exciton was estimated to be around 0.27 to 0.31 0 . These results are consistent with the value reported in ab initio calculations 42,43 .…”

Interaction-Induced Shubnikov–de Haas Oscillations in Optical Conductivity of Monolayer MoSe2

“…Moreover, spinvalley locking by the spin-orbit coupling [18] as well as the presence of the valley-contrasting π Berry phase [12] give rise to a unique ladder of spin-and valley-polarized LLs in TMD monolayers [19,20], the degeneracy of which is further lifted by the strong Zeeman effect [21,22]. Although the fingerprints of such LLs have been recently reported in several transport experiments [23][24][25][26][27][28], their optical signatures have been obtained only for the WSe 2 monolayer at high electron densities, where exciton binding is suppressed due to screening; in this limit, the optical excitation spectrum is similar to that of GaAs 2DES at moderate fields and shows band-to-band inter-LL transitions [29].…”

Zeeman spectroscopy of excitons and hybridization of electronic states in few-layer WSe 2 , MoSe 2 and MoTe 2

“…An externally applied magnetic field in the Faraday geometry lifts the valley degeneracy, resulting in a so-called valley Zeeman splitting [1]. Therefore, the g-factors of the excitons can be measured using helicity-resolved spectroscopy under magnetic fields [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In multilayer and bulk TMDCs, it has been found that the spin orientation of the carriers is strongly coupled to the valleys within the individual layers ("spin-layer locking") [17,[19][20][21].…”