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Abstract Many unusual and promising properties have been reported recently for the transition metal trichalcogenides of the type MPS3 (M = V, Mn, Fe, Ni ...), such as maintaining magnetic order to the atomically thin limit, ultra-sharp many-body excitons, metal-insulator transitions and, especially for Fe2P2S6, giant linear dichroism among others. Here we conduct a detailed investigation of the electronic structure of Fe2P2S6 using angle-resolved photoemission spectroscopy, q-dependent electron energy loss spectroscopy, optical spectroscopies and density functional theory. Fe2P2S6 is a Mott insulator with a gap of E gap ≈ 1.4 eV and zigzag antiferromagnetism below T N = 119 K. The low energy excitations are dominated by Fe 3d states. Large and sign-changing linear dichroism is observed. We provide a microscopic mechanism explaining key properties of the linear dichroism based on the correlated character of the electronic structure, thereby elucidating the nature of the spin-charge coupling in Fe2P2S6 and related materials.

Cr_{2}Ge_{2}Te_{6} is a quasi-two-dimensional semiconducting van der Waals ferromagnet down to the bilayer with great potential for technological applications. Engineering the critical temperature to achieve room-temperature applications is one of the critical next steps on this path. Here, we report high-resolution capacitance dilatometry studies on Cr_{2}Ge_{2}Te_{6} single crystals which directly prove significant magnetoelastic coupling and provide quantitative values of the large uniaxial pressure effects on long-range magnetic order (∂T_{C}/∂p_{c}=24.7 K/GPa and ∂T_{C}/∂p_{ab}=−15.6 K/GPa) derived from thermodynamic relations. Moderate in-plane strain is thus sufficient to strongly enhance ferromagnetism in Cr_{2}Ge_{2}Te_{6} up to room temperature. Moreover, unambiguous signs of short-range magnetic order up to 200 K are found.

Two-dimensional magnetic materials with tunable physical parameters are emerging as potential candidates for topological phenomena as well as applications in spintronics. The famous Mermin-Wagner theorem states that spontaneous spin symmetry cannot be broken at finite temperature in low dimensional magnetic systems which forbids the possibility of a transition to a long-range ordered state in a two-dimensional magnetic system at finite temperature. Though, there are some exceptions to Mermin-Wagner theorem in particular low dimensional magnetic systems with topologically ordered phase transitions. Here, we present an in-depth temperature dependent analysis for the bulk single crystals of two-dimensional (Mn 1-x Ni x ) 2 P 2 S 6 with x = 1, 0.7, 0.3, 0 using the Raman spectroscopy supported by first-principles calculations of the phonon frequencies. We observed multiple phase transitions with tunability as a function of doping associated with the short and long-range spin-spin correlations. First transition at ~ 150 K to ~ 170 K for x = 0 to x = 0.7, and second one from ~ 60 K to ~ 153 K. Quite interestingly, a third transition is observed at low temperature (much below their respective T N ) ~ 24 K to ~ 60 K and is attributed to the potential topological phase transition. These transitions are marked by the distinct changes observed in the temperature evolution of the phonon self-energy parameters, modes intensity and dynamic Raman susceptibility., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Topological superconductivity is a promising concept for generating fault-tolerant qubits. Early experimental studies looked at hybrid systems and doped intrinsic topological or superconducting materials at very low temperatures. However, higher critical temperatures are indispensable for technological exploitation. Recent angle-resolved photoemission spectroscopy results have revealed that superconductivity in the type-I Weyl semimetal-trigonal PtBi 2 (t-PtBi 2 )-is located at the Fermi-arc surface states, which renders the material a potential candidate for intrinsic topological superconductivity. Here we show, using scanning tunnelling microscopy and spectroscopy, that t-PtBi 2 presents surface superconductivity at elevated temperatures (5 K). The gap magnitude is elusive: it is spatially inhomogeneous and spans from 0 to 20 meV. In particular, the large gap value and the shape of the quasiparticle excitation spectrum resemble the phenomenology of high-T c superconductors. To our knowledge, this is the largest superconducting gap so far measured in a topological material. Moreover, we show that the superconducting state at 5 K persists in magnetic fields up to 12 T., Competing Interests: Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity 1,2 . As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity 3 , making systems fragile and difficult to realize 4-7 . Due to their intrinsic topology 8 , Weyl semimetals are also potential candidates 1,2 , but have always been connected with bulk superconductivity, leaving the possibility of intrinsic superconductivity of their topological surface states, the Fermi arcs, practically without attention, even from the theory side. Here, by means of angle-resolved photoemission spectroscopy and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material trigonal PtBi 2 (ref.  9 ). We show these states become superconducting at temperatures around 10 K. Remarkably, the corresponding coherence peaks appear as the strongest and sharpest excitations ever detected by photoemission from solids. Our findings indicate that superconductivity in PtBi 2 can occur exclusively at the surface, rendering it a possible platform to host Majorana modes in intrinsically topological superconductor-normal metal-superconductor Josephson junctions., (© 2024. The Author(s).)

An ultrasharp photoluminescence line intimately related to antiferromagnetic order has been found in NiPS_{3}, a correlated van der Waals material, opening prospects for magneto-optical coupling schemes and spintronic applications. Here we unambiguously clarify the singlet origin of this excitation, confirming its roots in the spin structure. Based on a comprehensive investigation of the electronic structure using angle-resolved photoemission and q-dependent electron energy loss spectroscopy as experimental tools we develop, in a first step, an adequate theoretical understanding using density functional theory (DFT). In a second step the DFT is used as input for a dedicated multiplet theory by which we achieve excellent agreement with available multiplet spectroscopy. Our Letter connects the understanding of the electronic structure and of optical processes in NiPS_{3} and related materials as a prerequisite for further progress of the field.

Symmetry breaking in topological matter has become in recent years a key concept in condensed matter physics to unveil novel electronic states. In this work, we predict that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi 2 lead to a type-I Weyl semimetal band structure. Transport measurements show an unusually robust low dimensional superconductivity in thin exfoliated flakes up to 126 nm in thickness (with T c ∼ 275-400 mK), which constitutes the first report and study of unambiguous superconductivity in a type-I Weyl semimetal. Remarkably, a Berezinskii-Kosterlitz-Thouless transition with T BKT ∼ 310 mK is revealed in up to 60 nm thick flakes, which is nearly an order of magnitude thicker than the rare examples of two-dimensional superconductors exhibiting such a transition. This makes PtBi 2 an ideal platform to study low dimensional and unconventional superconductivity in topological semimetals.

Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (k F ) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of k F -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opportunities for high-resolution ARPES in the physical and life sciences., (© 2022. The Author(s).)