Tuning Quantum Materials

Quantum materials, which often exhibit collective orders such as antiferromagnetism, charge-density waves, or superconductivity, tend to react sensitively to small changes of external parameters, including temperature, magnetic field, composition, or lattice parameters. The use of such parameters thus permits control and tuning of the materials’ properties. I will first discuss examples of strain acting as a control parameter and probe for physical properties in materials such as CsFe₂As₂ or Ca_1-xSr_xCo₂As₂. We investigate both thermal strains and the effect of externally applied strains using thermal-expansion and elastoresistance measurements. Second, I will discuss chemical tuning. The close integration of single-crystal synthesis techniques with transport and thermodynamic methods permits us to identify the consequences of small chemical variations. For example, I will show how the charge-density-wave transition in NbSe2 is modified when crystal-growth conditions vary.