Spin Resolved Scanning Tunneling Spectroscopy

Siwat PolinPh.D Candidate ,School of Physics ,SUT

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Solid state Spectroscopy SP-STS: part 1

Outline1. Scanning Tunneling Microscopy (STM)

2. Scanning Tunneling Spectroscopy (STS)

3. Spin Resolved Scanning Tunneling Spectroscopy (SR-STS)

4. SR-STS Components

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Scanning Tunneling Microscope

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Quantum mechanic of tunneling

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Scanning Tunneling Spectroscopy

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By ramping the bias voltage,or distance of tip from surface,the current signal can reveal the local electronic character of the surface.

Can determine:-Conductivity-Bandgap-Work function-Density of state

STS measurements consist in measuring the tunneling current I as a function of the bias voltage V applied between tip and sample.The tunneling current can be expressed as:

With ρs and ρT the density of states of sample and tip respectively, and T the transmission probability. Keeping the tip density of states ρT constant and taking the first derivative of I(V) with respect to the bias voltage V:

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High Tcsuperconductor

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Spin Resolved Scanning Tunneling Spectroscopy

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Spin Resolved Scanning Tunneling Spectroscopy

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Spin Resolved Scanning Tunneling Spectroscopy

TMR : Tunnel Magnetoresistance

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SP-STM modes of operation

1.Constant current mode

2.Spin-resolved spectroscopic mode

3.Modulated tip magnetization

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Atomic resolution of antiferromagnetic Mn on W(110)

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Antiferromagnetic tip

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Figure representation of Sp-STM Tip electrodes, a) for measuring the out-of-plane and b) the in-plane component

a) Optical image of a ring electrode (outer diameter : 2 mm, inner diameter: 0.7 mm) as used for Sp-STM measurement b) SEM image taken at the outer perimeter of a ring where tunneling can occur

Differential magnetic mode

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Tip is periodically switch at 20-40 KHz

Electric circuit of the Sp-STM with the separation of topology and spin signal

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Basic Components

1.Metal Tip2.Piezoelectric scanner3.Current Amplifier(nA)4.Bipotentiostat(bias)5.Feedback loop (current)6.Vibration isolator

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Metal Tip

Commercial STM probe tip

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Piezoelectric scannerTip holder ,Sample holder

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Current amplifier,Feedback loop

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-Tunneling current between tip and sample is detected with I-V converter and is amplified with current amplifier.-Feedback loop adjust s z coordinate such that the tunneling current is equal to the set point.

Bipotentiostat

Vibration isolator

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Chamber

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Variable temperature STM (VT-STM)

The cryogenic STM

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InstrumentA. Overall system layoutB. Vibration and acoustic isolation

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stage vibration isolation

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Acoustic box

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LT-STM setup, all facilities for insitu preparation of magnetic molecular surfaces as well as magnetic tips are installed. The experiments are performed at 7 K with magnetic fields available to control the in-plane magnetism (upto 2 Tesla) and out-of-plane magnetism (upto 6 Tesla). Once the sample is installed, the contamination level is as low as 1 adsorbate per 1 micrometer per 1 week

High stability scanning tunneling spectroscopy and spin-polarized scanning tunneling microscopy

The whole setup rests on damping legs for mechanical isolation. The dewar system to maintain the operation temperature is located below the vacuum system and built into the ground. Respectively, samples are loaded from

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THANK YOU FOR YOUR ATTENTION

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