Scanning Tunneling Microscope in a Dilution Refrigerator with a Vector Magnetic Field Solenoid J. Galvis, I Guillamón, H Suderow, J. G. Rodrigo, S. Viera Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia condensada Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain Cryoconference 2010 - Young researchers
OUTLINE 1. SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY MIXED STATE SUPERCONDUCTIVITY STUDY WITH STM LAYERED SUPERCONDUCTORS 2. EXPERIMENTAL TECHNIQUES CRYOSTAT DESCRIPTION STM DESCRIPTION VECTOR MAGNETIC FIELD SOLENOID OVERVIEW 3. PERSPECTIVES
MIXED STATE TYPE I SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY TYPE II Abrikosov hexagonal lattice NORMAL The magnetic field penetrates in form of vortices. Coherence length ONE OF THE MAIN MOTIVATIONS FOR THE DEVELOPMENT OF THIS EXPERIMENTAL SETUP IS THE STUDY OF MIXED STATE IN SOME SUPERCONDUCTORS.
SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY SUPERCONDUCTIVITY STUDY WITH STM ACOORDING TO TERSOFF AND HAMMAN THE TUNELLING CURRENT BETWEEN TWO ELECTRODES: TUNELLING CURRENT BETWEEN NORMAL METAL AND SUPERCONDUCTOR MATERIAL: TUNELLING CONDUCTANCE: Simplified form assuming N 1 constant. J. Tersoff, and D. R. Hamann.. Phys. Rev. Lett., 50 (1985). DENSITY OF STATE
SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY SUPERCONDUCTIVITY STUDY WITH STM How can we built the vortex lattice map of density of states? TIP D D SAMPLE DOS is obtained measuring the tunneling conductance. SAMPLE Magnetic field perpendicular to surface VORTEX Scanning the entire sample surface makes it possible to build the vortex lattice. V. Crespo.Superconductividady magnetismoa travésde la espectroscopíatúnel de barrido con punta superconductora. PHD Thesis. Universidad Autónoma de Madrid.
LAYERED SUPERCONDUCTORS SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY 2H DICHALCOGENIDES FAMILY CRYSTAL STRUCTURE Characterized by Transition metal Chalcogenide 2H REPRESENTS A HEXAGONAL SIMMETRY AND TWO LAYERS PER UNIT CELL. THE X-M-X BLOCKS ARE WEAKLY BONDED BY VAN DER WAALS FORCES. Initial objective THE CRYSTAL STRUCTURE IS STRONGLY 2-DIMENSIONAL.
LAYERED SUPERCONDUCTORS SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY Why is the vortex lattice of the NbSe 2 system interesting? The six rays can be interpreted as directions in which the coherence length diverges, caused by local Fermi surface anomalies in these directions. The vortex exhibit a star shape with six rays. A sharp peak appears Localized states in the vortex core I. Guillamon. Orden y desorden en superconductividad. PHD Thesis. Universidad Autónoma de Madrid. The peak is shifted to higher energies
SUPERCONDUCTIVITY AND TUNNELING MICROSCOPY LAYERED SUPERCONDUCTORS Anisotropic superconductors VARIOUS BUCKLING INSTABILITES ARE OBSRVED For large angles and high energy the star shape vanish
CRYOSTAT DESCRIPTION CRYOSTAT DESCRIPTION 1K POT STILL CONTINUOS HEAT EXCHANGER STEP HEAT EXCHANGER MIXING CHAMBER
CRYOSTAT DESCRIPTION CRYOSTAT DESCRIPTION STM THE STM IS ATTACHED AND THERMALIZED WITH THE MIXING CHAMBER
CRYOSTAT DESCRIPTION CRYOSTAT DESCRIPTION CABLES BRAID AND SHIELDED CABLES. 8 CABLES OF MANGANIN AND 8 CABLES OF COPPER. Twisted pair cable
CRYOSTAT DESCRIPTION CRYOSTAT DESCRIPTION CABLES THERMALIZATION 1K POT STILL CONTINUOS HEAT EXCHANGER The gold plates are bolted to the cryostat. MIXING CHAMBER The cable is trapped between two gold plates.
STM DESCRIPTION STM DESCRIPTION Z MOTION QUICK SLOW Mobile Internal generation of a mechanical force resulting from an applied electric field. Sample Piezoelectric material
STM DESCRIPTION Piezotube cross section Sample The displacement of the tip over the sample is determined by the piezotube characteristic and applied voltage. Maximum displacement:
STM DESCRIPTION The sample holder is set on a moving part, which can be moved from the outside of cryostat through a piano wire attached to a precision screw. Rotating the Removable precision screw piece the sample holder moves. The spring allows that the sample return to its initial position. Sample holder Skate Piano wire
STM DESCRIPTION Macroscopic motion over the sample at 100 mk In conclusion macroscopic motion of the screw, allows a microscopic movement of the sample holder. FIB milledpathsin Au substratein a zigzag shape. Three images corresponding to three steps of the sample holder I. Guillamon. Orden y desorden en superconductividad. PHD Thesis. Universidad Autónoma de Madrid.
STM DESCRIPTION STM CONTROL SYSTEM Piezotube signal X Y Z Current amplifier Voltage supply Electronic Control Digital-Analog converter LuNi 2 B 2 C
VECTOR MAGNETIC FIELD SOLENOID VECTOR MAGNETIC FIELD SOLENOID 0-5 TESLA IN Z DIRECTION 0-1,2 TESLA IN THE X-Y PLANE The STM is located just in the geometrical center of the coils. X Y X
VECTOR MAGNETIC FIELD SOLENOID AXIAL MAGNETIC FIELD TRANSVERSAL MAGNETIC FIELD
OVERVIEW INSERT 5 meters STM CONTROL SYSTEM HOME- MADE GAS HANDLING SYSTEM HOME- MADE POWER SUPPLY FOR VECTOR MAGNETIC FIELD SOLENOID ALL PUMPS ARE IN OTHER ROOM AWAY OF THE INSERT. PUMP ROOM -100 to 100A X 3 In construction
PERSPECTIVES TO STUDY THE VORTEX LATTICE IN DICHALCOGENIDES WITH RESPECT TO MAGNETIC FIELD ANGLE, IN PARTICULAR THE SYSTEM NbSe 2. TO STUDY THE SHAPE OF THE VORTEX CORE WITH RESPECT TO MAGNETIC FIELD ANGLE.
BIBLIOGRAPHY H. F. Hess, R. B. Robinson, and J. V. Waszczak Phys. Rev. Lett. 64, 2711 (1990) H. F. Hess, C. A. Murray and J. V. Waszczak Phys. Rev. B. 22, 636 (1994) V. L. Ginzburg. Superconductivity. World Scientific. 2004 V. Crespo. Superconductividad y magnetismo a través de la espectroscopía túnel de barrido con punta superconductora. PHD Thesis. Universidad Autónoma de Madrid (2009). I. Guillamon. Orden y desorden en superconductividad. PHD Thesis. Universidad Autónoma de Madrid (2009). I. Guillamón, H. Suderow, S. Vieira, L. Cario, P. Diener, and P. Rodière, Phys. Rev. Lett. 101, 166407 (2008) M. Tinkham, Introduction to Superconductivity. Dover Publications. Second edition (2004) J. Tersoff, and D. R. Hamann.. Phys. Rev. Lett., 50 (1985)