The discussion centers on the challenges of detecting electron spin resonance (ESR) in metals, particularly concerning free electrons. Participants agree that due to the continuum of energy levels in free electrons, identifiable ESR signals are unlikely. The conversation references key studies, including the 1955 papers by Feher and Dyson, which detail the complexities of observing conduction electron spin resonance (CESR) in metals, emphasizing the need for discrete energy levels and the impact of skin depth on signal detection. It is concluded that while ESR is feasible in certain conditions, typical bulk metals present significant challenges due to broadening effects and low relaxation times.
PREREQUISITESPhysicists, materials scientists, and researchers involved in electron spin resonance studies, particularly those focusing on metals and conductive materials.
I saw some hits about that. However, the conduction mechanism is not the same as in a straight metal and I am pretty sure that you would need discrete energy levels in order to be able to identify lines and the broadening due to applied fields.Fred Wright said:A quick search gave this at the top of the list: https://www.researchgate.net/publication/230752244_EPR_study_of_conduction_electrons_in_heavily_doped_n-type_4H_SiC
It's an interesting lead, as I'm searching for an experimental protocol. I should have to "stabilize" the free electrons (I don't yet know how, but I don't need sharp lines, it's just to test a vague idea with the purpose of using it in classical electromagnetism).sophiecentaur said:...I am pretty sure that you would need discrete energy levels in order to be able to identify lines and the broadening due to applied fields.
As far as I'm aware, spin resonance is what happens to a single energy level when there is an applied magnetic field. If there is no 'single level' (i.e. vast numbers of electrons with the same level), then how can a split be detected?Exnihiloest said:It's an interesting lead, as I'm searching for an experimental protocol. I should have to "stabilize" the free electrons (I don't yet know how, but I don't need sharp lines, it's just to test a vague idea with the purpose of using it in classical electromagnetism).
Yes. I agree what the Zeeman effect is about but surely you need to have a population of atoms with defined energy levels in order to observe this. OR is the method to observe a transition between the two levels directly? That could make sense and the ΔE could correspond to a much lower (RF) frequency which would be similar for a whole range (band?) of energy states for the electrons. I am having a problem in identifying this as a 'Zeeman effect' because the original energy states of free electrons are extremely low magnitude.marcusl said:The relevant energy levels are the two Zeeman levels created by the magnetic field. The resonance condition is given by the energy difference between a spin aligned and anti-aligned with the field. The background behavior of the electrons can indirectly affect the resonance, mainly through coupling and its effect on relaxation time, but the resonance condition is set by the B field.
EDIT: Having said that, I imagine it would be hard to do EPR in an ordinary bulk metal due to the minuscule skin depth at micro- or millimeter-waves. You will be looking primarily at oxides and surface states.
OK. You put the atoms in a cavity and look for a resonance at the `Larmor Frequency. Have you done that? On the face of it, I guess it should work.marcusl said:Microwave photons induce transitions between the Zeeman states, or classically, the MW field causes the spins to process at the Larmor frequency set by the B field. As I said, the election energy is irrelevant to first order.
I never spoke of stabilizing electrons (whatever that may be), that was someone else.
There’s no need to guess; in the 74 years since EPR was first demonstrated, it has both been shown to “work” over and over, and been thoroughly explained using sound physics principles.sophiecentaur said:On the face of it, I guess it should work.
Ah well. The only (afair) mention of this in my degree course was in the context of the Zeeman effect. I should not fire from the hip in these matters. Sorry.marcusl said:There’s no need to guess; in the 74 years since EPR was first demonstrated, it has both been shown to “work” over and over, and been thoroughly explained using sound physics principles.
sophiecentaur said:OK. You put the atoms in a cavity and look for a resonance at the `Larmor Frequency. Have you done that? On the face of it, I guess it should work.
f95toli said:Electrons that are completely free to move would as far as I understand never be spin active.
Those two posts seem to be saying different things. what is the real situation?marcusl said:There’s no need to guess; in the 74 years since EPR was first demonstrated, it has both been shown to “work” over and over, and been thoroughly explained using sound physics principles.
The fact that you do not incidentally see a signal in an apparatus that is not tuned for the purpose is not proof that the measurement is impossible. (A quadruple negative, oh dear...) On the contrary, there is a significant body of papers that present EPR data taken on conduction electrons in metals. The earliest complete experimental and theoretical report is from 1955, and it includes spectra on a variety of metals at temperatures from room temperature down to 4K.f95toli said:I'm not sure I follow. If the question is if you will see a defined peak in an ESR spectra from conduction electrons in an ordinary metal the answer is no (and I am speaking from experience here; I do ESR measurement as part of my work and my sample holders are made from metal ). You can (obviously) use ESR to study e.g. rare-earth ions in solids (typically the ions are impurities in some sort of dielectric) but the point is that these are quite well separated from each other.
Electrons that are completely free to move would as far as I understand never be spin active.