Calorimetric Tunneling Spectroscopy as a Perspective Tool for Derivation of Energy-spectroscopic Information in Electrically Conductive Solids

Abstract

We discuss basic principles of a novel experimental technique, calorimetric tunneling spectroscopy (CTS), based on precise measurements of the heat generated due to electron tunneling in vacuum barrier tunneling junctions (VBTJs). We argue that CTS represents an alternative/complementary experimental method to the classical electron tunneling spectroscopy capable to yield equivalent physical information. : 73.40.Gk, 73.90.+f Careful measurements of the current-voltage (I-V ) characteristics of tunneling junctions (TJs) can be used for the derivation of energy-spectroscopic information of solids [1]. Many types of TJs, among them VBTJs (Fig. 1a) and TJs with insulating barrier (Fig. 1b), were used for the determination of electronic densities of states (DOS) or inelastic excitation thresholds from measured voltage dependence of dI/dV or d 2 I/dV 2 , respectively [1]. As well, measured d 2 I/dV 2 spectra of small metal constrictions (Fig. 1c) by means of point contact (PC) spectroscopy can contain structures which well correlate with phonon spectra of studied metals and can be related to the Eliashberg coupling function g(ω) = α 2 F (ω) [2]. PACSUnfortunately, PC spectroscopy works well only in systems in which the dimension d of the contact is smaller than the mean free path l of electrons (d < l). This presents serious limitation for a more wide utilization of the PC spectroscopy in the modern solid state physics, where systems with very short mean free path are frequently studied (e.g. heavy fermions or valence fluctuating systems). This limitation can be overcome if PCs operate in the tunnel regime [3]. As shown in [3], PC spectra in which metal electrodes are separated by thin insulating barrier (e.g. as depicted in Fig. 1b) with not too low barrier transmission probability still yield an information about the electron-phonon interaction (EPI), and moreover, in contrast to PCs in the ballistic regime, they do not require satisfaction of inequality d < l [3].If the voltage is applied across a PC with large Knudsen ratio K = l/d, then the electric field is confined to regions of dimension d of the contact [4]. Carriers * ) Presented at 12