Momentum-dependent scanning tunneling spectroscopy in MgB{sub 2}. Page: 2 of 3
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Momentum-Dependent Scanning Tunneling Spectroscopy in MgB2
Goran Karapetrov al, Maria Iavarone a, A.E. Koshelev a, W.K. Kwok a, G.W. Crabtree a,
D.G. Hinks a, S.I. Lee ,
aMatertals Sc0ence Drmson, Argonne National Laboratory, Argonne, IL 60439, USA
bNCRICS and Department of Phystcs, Pohang Unwerstty of Sctence and Technology, Pohang 790-784, Repubhc of KoreaAbstract
We present study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy
and spectroscopy. The results reveal two distinct energy gaps at A1=2.3 meV and A2=7.1 meV. Different spectral
weights of the partial superconducting density of states are a reflection of different tunneling directions in this
multi-band system. Our experimental observations are consistent with the existence of two-band superconductivity
in the presence of interband superconducting pair interaction and quasiparticle scattering. Temperature evolution
of the tunneling spectra follows the BCS scenario with both gaps vanishing at the bulk T. The data confirm the
importance of Fermi-surface sheet dependent superconductivity in MgB2 proposed in the multigap model by Liu
et al. [1]Key words: MgB2; STM; scanning tunneling spectroscopy; multi-gap superconductivity
1. Introduction
The discovery of superconductivity in MgB2 [2] at
39K sparked great interest in the fundamental physics
and practical applications of this material. Two-gap
scenario has been predicted theoretically by Liu et
al. [1]. First principle calculations show that the Fermi
surface of MgB2 consists of 2D cylindrical sheets aris-
ing from - antibonding states of B p, orbitals, and 3D
tubular networks arising from 7r bonding and antibond-
ing states of B p orbitals. In this theoretical frame-
work [1] two different energy gaps exist, the smaller
one being an induced gap associated with the 3D bands
and the larger one associated with the superconduct-
ing 2D bands. Furthermore both superconducting gaps
should vanish at the bulk critical temperature T.
Scanning tunneling spectroscopy is a unique tech-
nique that allows direct measure of the DOS near
the Fermi energy and since the contribution to the
tunneling conductivity of electronic states with finite
1 Corresponding author. E-mail: goran@anl.govmomentum in the tunneling direction is exponentially
larger than the contribution of states with momen-
tum perpendicular to tunneling direction, the STM
can distinguish between the 2D bands with little or
no c-axis component of Fermi velocity and 3D bands
with considerable c-axis component. In the clean
limit(l 27rH) the direction of the tunneling current
selects which band and which superconducting gap
is probed. In this paper we report direct evidence
of orientation-dependent double-gap structure in the
quasi-particle energy spectra as determined from tun-
neling spectroscopy.
2. Results
Compact samples of MgB2 were synthesized from
amorphous B powder (4N's purity) and high purity Mg.
The B powder was pressed into pellets under 6 kbar
pressure. These pellets were reacted with Mg vapor at
850 C for 2 hr in a BN container under 50 bar of Ar.
The typical critical temperature of these gold-coloredPreprint submitted to LT23 Proceedings
21 June 2002
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Karapetrov, G.; Iavarone, M.; Koshelev, A. E.; Kwok, W. K.; Crabtree, G. W.; Hinks, D. G. et al. Momentum-dependent scanning tunneling spectroscopy in MgB{sub 2}., article, July 31, 2002; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc738252/m1/2/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.