Computational Solid State Physics 計算物性学特論 第10回 10. Transport properties II: Ballistic transport
Electron transport properties l e : electronic mean free path l φ : phase coherence length λ F : Fermi wavelength
Tunneling transport I L
Current in one-dimension T(k): transmission coefficient
Total current in one-dimension
Low bias limit : conductance at low temperatures
Landauer ’ s formula : transmission coefficient : Conductance : Quantum conductance : Quantum resistance I: current, V: bias
Two- and four- terminal measurements
Tow- and four- terminal measurement 2-terminal measurement 4-terminal measurement
Conductance of a quantum point contact
Only one channel (n=1) is open. for n=1 Conductance of a quantum point contact Quantization of transverse motion
Nanowire of Au
Mechanically Controllable Break Junction
Histogram of conductance of a relay junction
Conductance through a quantum dot
:Lorentzian broadening of resonant tunneling through quantized energy E N of a dot :Thermal broadening Tunneling current via quantum dot
A bound state and a resonant state
Transmission coefficient for resonant tunneling If T L =T R
Transmission coefficient of a resonant-tunneling structure
Characteristics of resonant tunneling diode
Resonant tunneling current :wave function :energy
Large bias and low temperature limit Total resonant tunneling current
Transmission coefficient for resonant tunneling If T L =T R
Profile through a three-dimensional resonant-tunnelling diode. The bias increases from (a) to (d), giving rise to the I(V) characteristic shown in (e). The shaded areas on the left and right are the Fermi seas of electrons. Profile through a three-dimensional resonant tunneling diode
Problems 10 Calculate the density of states for free electrons in one, two and three dimensions. Calculate the ballistic current in two dimensions. Calculate the transmission coefficient for a square barrier potential. Calculate the transmission coefficient for a double square barrier potential.