Dynamical Metal to Charge-Density-Wave Junctions in an Atomic Wire Array

Abstract

We investigated the atomic scale electronic phase separation emerging from a quasi-1D charge-density-wave (CDW) state of the In atomic wire array on a Si(111) surface. Spatial variations of the CDW gap and amplitude are quantified for various interfaces of metallic and insulating CDW domains by scanning tunneling microscopy and spectroscopy (STS). The strong anisotropy in the metal−insulator junctions is revealed with an order of magnitude difference in the interwire and intrawire junction lengths of 0.4 and 7 nm, respectively. The intrawire junction length is reduced dramatically by an atomic scale impurity, indicating the tunability of the metal−insulator junction in an atomic scale. Density functional theory calculations disclose the dynamical nature of the intrawire junction formation and tunability.

Ultrafast Probing and Coherent Vibrational Control of a Surface Structural Phase Transition

“…In the first case, the boundary separates metallic and insulating domains within a single In wire and typically extends over about 7 nm. In the case of an inter-wire junction, however, this characteristic length is significantly reduced to less than 0.5 nm, underlining the quasi-one-dimensional nature of the atomic wire array [234]. A similar reduction of the junction length is found for adatom/defect-induced domain boundaries.…”

“…Within the last 30 years the Si(111)(4×1)-In surface has become a model system to study electronic and thermal transport [256], phase transitions [102,107,117,237] as well as atomic scale defects [234] and fluctuations [257,258] in low-dimensional materials. Since its discovery, the (4×1) phase has been examined by a large number of different experimental methods, including LEED [117,259], I(V)-LEED [195], RHEED [116,260,261], reflective high-energy positron diffraction (RHEPD) [262], X-ray diffraction (XRD) [263], angle-resolved photoemission spectroscopy (ARPES) [12,153,250], Core-level PES [264], Auger-electron spectroscopy (AES) [260], electron energy loss spectroscopy (EELS) [265,266], reflectance anisotropy spectroscopy (RAS) [267][268][269][270], Raman spectroscopy [240,269,271], electrical transport measurements [261,272], and STM [125,234,255,[273][274][275]. From a theory perspective, the system has been investigated by density functional theory (DFT) [276,277] and other approaches…”

“…In addition to the microscopic mechanisms underlying the phase transition and the coupling of electron and phonons therein, the question of whether the transition is of first or second order has been discussed intensively 16 . At the atomic level, STM has provided unambiguous evidence for the coexistence of (4×1) and (8×2) phases well below T c [234,257,278,298], pointing to a first-order transition (for details about surface heterogeneity see Sec. 4.5).…”

“…Besides its ultrafast dynamics, the Si(111)(8×2)-In surface has attracted significant attention for a variety of atomic scale phenomena, including phase coexistence [257,298], dynamical metal-to-CDW junctions [234], defect-induced charge ordering [278] and pinning [283], or chiral solitons [125]. While a direct observation of these effects requires atomic-scale real-space imaging and spectroscopy as provided exclusively by STM and STS, signatures of local surface inhomogeneities may as well influence the results of spatially averaging techniques such as LEED, depending on their density and long-range order.…”

“…Furthermore, a number of different adatoms or adsorbed molecules can either pin the (4×1) phase locally [261], modify the local charge-order [278] or lead to various types of intrachain defects 23 and domain boundaries [125,275,299]. Domain boundaries between (4×1) and (8×2) phases represent atomic-scale metalinsulator junctions and have been investigated in a number of combined STM and DFT studies, with regard to their atomic and electronic structure, as well as dynamics and fluctuations [234,257,298]. Junctions are formed both along and perpendicular to the indium wires.…”