The curves are normalized to the resistivity measured at RT and the vertical dashed lines show the location of T c for each doping as determined using ARPES. The inset shows T-dependent resistivity curves measured on the pristine (red curve) and Ti-doped crystals. The CDW transition temperature T c is linearly decreasing with x towards a QCP. (c) T − x phase diagram of Ti-doped 1 T − TiSe 2. The red-dashed lines locate the critical CDW transition temperatures ( T c) extracted from the energy shift of the Se 4 p backfolded band (blue dots) Δ E backf as a function of T using a BCS-type gap equation as shown in (b). For each doping, lower and upper panels respectively show the RT and LT EDCs. (a) T-dependent EDC maps measured at L as a function of Ti self-doping (from left to right). (g) Linear dependence of the experimental chemical-potential shift Δ μ with x as extracted from the evolution of the hole and electron band extrema.
Blue-, respectively red-, dashed lines and triangles in (e) and (f) correspond to parabolic fits of the maxima of the MDC curves (triangles). (e),(f) RT ARPES intensity maps, as false color plots (blue colors represent strong intensity) as a function of x at the A and L points of the BZ.
IN THE VICINITY WINDOWS
The blue- and red-dashed boxes respectively indicate the energy and k x windows shown in (e) and (f) for the hole and electron pockets. (d) Large–energy scale ARPES spectrum of pristine along the k y = 0 Å − 1 cut of the FS. Also indicated is the in-plane component of the CDW q vector.
The k x axis depicted in (b) and (c) by the black arrow is the A − L direction of the BZ. (c) RT Fermi surface (FS) of pristine 1 T − TiSe 2 as measured using He I radiation ( h ν = 21.22 eV). IAlso shown is one CDW q vector, q C D W, that connects the Γ and one of the L points at the phase transition. (b) Three-dimensional Brillouin zone (BZ) of 1 T − TiSe 2. Se up and Se down respectively refer to atoms of the top and bottom Se atomic planes of a 1 T − TiSe 2 layer. (a) Side view of two 1 T − TiSe 2 layers separated by a van der Waals gap. We therefore demonstrate an intimate relationship between the FS topology and the emergence of spatially textured electronic phases which is expected to be generalizable to many doped CDW compounds. We find an intrinsic tendency towards electronic PS in the vicinity of Fermi surface (FS) “hot spots,” i.e., locations with band crossings close to, but not at the Fermi level. Using angle-resolved photoemission spectroscopy and variable-temperature scanning tunneling microscopy, we report on the phase diagram of the CDW in 1 T − TiSe 2 as a function of Ti self-doping, an overlooked degree of freedom inducing CDW texturing.
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Although it has been recently proposed that the emergence of superconductivity relates to CDW fluctuations and the development of spatial inhomogeneities in the CDW order, the fundamental mechanism underlying such a phase separation (PS) is still missing. Prototypical materials are transition-metal dichalcogenides (TMDCs) and among them, 1 T − TiSe 2 exhibiting intertwined CDW and superconducting states under Cu intercalation, pressure, or electrical gating.
Spatially inhomogeneous electronic states are expected to be key ingredients for the emergence of superconducting phases in quantum materials hosting charge-density waves (CDWs).
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