The layered material ZrSiTe is currently extensively investigated as a nodal-line semimetal with Dirac-like band crossings protected by nonsymmorphic symmetry close to the Fermi energy. A recent infrared spectroscopy study on ZrSiTe under external pressure found anomalies in the optical response, providing hints for pressure-induced phase transitions at ≈4.1 and ≈6.5 GPa. By pressuredependent Raman spectroscopy and x-ray diffraction measurements combined with electronic band structure calculations we find indications for two pressure-induced Lifshitz transitions with major changes in the Fermi surface topology in the absence of lattice symmetry changes. These electronic phase transitions can be attributed to the enhanced interlayer interaction induced by external pressure. Our findings demonstrate the crucial role of the interlayer distance for the electronic properties of layered van der Waals topological materials.Topological materials such as topological insulators [1], Dirac [2], Weyl [3][4][5] or line-node semimetals [6,7] are of great fundamental interest due to their exotic nature of electronic phases, and thus heavily investigated nowadays. They usually exhibit extraordinary material properties, for example, high carrier mobility and unusual magnetoresistance [8][9][10]. Topological non-trivial phases often occur in layered materials with weak interlayer bonding, where the single layers behave rather as isolated two-dimensional (2D) objects, enabling the exfoliation to atomically thin 2D crystals with numerous possible applications [11][12][13][14][15]. Since the forces between the layers of such structures are usually weak, they are highly compressible perpendicular to the layers, and a dimensional crossover from 2D to 3D can be induced by external pressure. Generally, layered materials are prone to pressure-induced phenomena, and electronic topological transitions [16] are expected to be induced [17][18][19] and were suggested to occur in layered BiTeBr [20], BiTeI [21, 22], 1T-TiTe 2 [23], and the group V selenides and tellurides Bi 2 Se 3 , Bi 2 Te 3 , Sb 2 Te 3 [24-27]. "Electronic transitions" in metals were first introduced by Lifshitz in 1960 as transitions where the topology of the Fermi surface (FS) changes as a result of the continuous deformation under high external pressure [16]. Examples for pressure-induced alterations of the FS topology are the conversion of an open Fermi surface, such as * These authors contributed equally.a corrugated cylinder-type Fermi surface typical for layered materials, to a closed one, or the appearance of a new split-off region of the FS. Importantly, the changes in the Fermi surface topology during such a so-called Lifshitz transition are not related to a change in the lattice symmetry [16].In this work we find indications for two Lifshitz transitions in the layered van der Waals material ZrSiTe under external pressure, resulting from the enhanced interlayer interaction. ZrSiTe belongs to the family of compounds ZrXY (X=Si, Ge, Sn and Y =O, S, Se, Te), which are...

We studied the effect of external pressure on the optical response of the nodal-line semimetal candidate ZrSiTe by reflectivity measurements. At pressures of a few GPa, the reflectivity, optical conductivity, and loss function are strongly affected in the whole measured frequency range (200-16500 cm −1 ), indicating drastic changes in the electronic band structure. The pressure-induced shift of the electronic bands affects both the intraband and interband transitions. We find anomalies in the pressure dependence of several optical parameters at the pressures Pc1≈4.1 GPa and Pc2≈6.5 GPa, suggesting the occurrence of two phase transitions of either structural or electronic type.

Understanding the intricate interplay between multiple electronic phases in quantum materials such as charge density wave (CDW), superconducting, and metallic phases is a challenging issue. Systematic introduction of pressure is one approach that has been used to probe this interplay. However, the influence of pressure together with the intricate interaction between electronic and lattice degrees of freedom can trigger complex structural evolution and distribution of various electronic phases at the atomic scale, the characterization of which demands high spatial resolution. We investigate the atomic-scale response of the charge density waves and the underlying atomic lattice in 1T -TaS 2 after exposure to hydrostatic pressure. High-resolution transmission electron microscopy images show that the CDW order parameter reacts with an elasticlike strain response to pressure-induced stacking faults and dislocations in the lattice. This is characterized by a proliferation of phase defects including CDW dislocations, discommensurations, and domain walls. Our results evidence the importance of pressure-induced lattice deformations and defects in modulating, stabilizing, or destroying electronic phases at the atomic scale.

Tungsten ditelluride WTe 2 is a type-II Weyl semimetal with electronic properties highly sensitive to external pressure, as demonstrated by the superconductivity emerging under pressure. Here we study the optical conductivity of the type-II Weyl semimetal WTe 2 under external pressure at room temperature. With increasing pressure, a pronounced spectral weight transfer occurs from the high-energy to the low-energy interband transitions, with drastic changes in the profile of the optical conductivity spectrum indicating a high sensitivity of the electronic band structure to external pressure. The detailed analysis of the pressure-dependent optical conductivity furthermore reveals anomalies at the pressures ∼2 and ∼4.5 GPa, where an electronic and a structural phase transition, respectively, were reported in the literature.