Julio Larrea Jiménez

The electronic topology of a material is generally described by its Bloch states and the associated band structure, and can be altered by electron–electron interactions. In metallic systems, the interactions are usually treated through the concept of quasiparticles. Here we investigate what happens if no well-defined quasiparticles are present and show that a topological semimetal phase can emerge from the material’s quantum critical state. Using the non-centrosymmetric heavy-fermion compound CeRu ₄ Sn ₆ , which is intrinsically quantum critical, we show that the topological phase exhibits a dome structure as a function of the magnetic field and pressure. To understand these results, we study a Weyl–Kondo semimetal model at a Kondo destruction quantum critical point. Indeed, it exhibits features in the spectral function that can define topological crossings beyond the quasiparticle picture. Our results outline the importance of the interplay of quantum critical fluctuations and symmetry to search for other emergent topological phases.

The accurate determination of thermal conductivity κ(T) in bulk materials at room temperature and above is crucial for evaluating their compatibility for specific applications. The 3ω technique is an established methodology for studying the thermal conductivity of thin films, becoming particularly suitable in the case of bulk specimens for T ≳ 300 K, where standard stationary techniques require significant corrections for radiative losses. Although this method has been employed in several works, it remains not widely adopted because its implementation demands considerable sophistication, including experiment design, thin film deposition techniques, and choices of the geometry of the current/heat transducer, electronics, and analytical treatment of the signals. Based on a critical review of the technique’s key technical aspects, this work provides practical support for a rapid and user-friendly implementation, from the design phase through to execution and analysis. We release a Python-based graphical user interface that supports a quantitative estimation of the investigated temperature profiles based on the geometrical parameters (width/length) of the deposited transducer (heater/thermometer metal line) before an experiment, guaranteeing an optimal design of the experimental conditions for each given material under scrutiny.

At the liquid–gas phase transition in water, the density has a discontinuity at atmospheric pressure; however, the line of these first-order transitions defined by increasing the applied pressure terminates at the critical point¹, a concept ubiquitous in statistical thermodynamics². In correlated quantum materials, it was predicted³ and then confirmed experimentally^4,5 that a critical point terminates the line of Mott metal–insulator transitions, which are also first-order with a discontinuous charge carrier density. In quantum spin systems, continuous quantum phase transitions⁶ have been controlled by pressure^7,8, applied magnetic field^9,10 and disorder¹¹, but discontinuous quantum phase transitions have received less attention. The geometrically frustrated quantum antiferromagnet SrCu₂(BO₃)₂ constitutes a near-exact realization of the paradigmatic Shastry–Sutherland model^12,13,14 and displays exotic phenomena including magnetization plateaus¹⁵, low-lying bound-state excitations¹⁶, anomalous thermodynamics¹⁷ and discontinuous quantum phase transitions^18,19. Here we control both the pressure and the magnetic field applied to SrCu₂(BO₃)₂ to provide evidence of critical-point physics in a pure spin system. We use high-precision specific-heat measurements to demonstrate that, as in water, the pressure–temperature phase diagram has a first-order transition line that separates phases with different local magnetic energy densities, and that terminates at an Ising critical point. We provide a quantitative explanation of our data using recently developed finite-temperature tensor-network methods^17,20,21,22. These results further our understanding of first-order quantum phase transitions in quantum magnetism, with potential applications in materials where anisotropic spin interactions produce the topological properties^23,24 that are useful for spintronic applications.